Developed as a Part of the - Human Evolution by The ...humanorigins.si.edu/sites/default/files/Teachers... · Malaria teacher guide Developed as a Part of the Teaching Evolution through

Malariateacher guide

Developed as a Part of the Teaching Evolution through Human Examples Project

SmithsonianNational Museum of Natural History

full version

Curriculum Development TeamPaul M. Beardsley, California State Polytechnic University, Pomona, Center for Excellence in Mathematics

and Science Teaching and Department of Biological Sciences, Lead AuthorBarbara Resch (Copyediting)

National Museum of Natural HistoryBriana Pobiner, Human Origins Program, Project Principal InvestigatorRick Potts, Human Origins Program, Project Co-Principal Investigator

Advisory CommitteeConstance Bertka, Science and Society Resources, LLCJuliet Crowell, National Science Resources Center, Smithsonian InstitutionJay Labov, National Academy of SciencesDennis Liu, Howard Hughes Medical InstituteSharon Lynch, The George Washington University, Graduate School of Education and Human DevelopmentLee Meadows, University of Alabama at Birmingham, Department of Curriculum and InstructionBill Watson, Office of Catholic Schools at the Diocese of Camden, Director of Curriculum and Assessment,

Senior Personnel and Data Analyst

Design TeamCarla Easter, National Human Genome Research InstituteK. David Pinkerton, Independent Education ConsultantMark Schwartz, Department of Population Health, NYU School of MedicineMark Terry, The Northwest School (Seattle, WA)Jennifer Clark, Human Origins Program, IllustratorNorma Oldfield, Human Origins Program, Illustration Research AssistantAnna Ragni, Human Origins Program, Illustration Research Assistant

© 2015 Smithsonian Institution. Permission to copy and distribute is freely granted for educational, noncommercial use only.

This material is based upon work supported by the National Science Foundation under Grant No. 1119468.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

contents 3

Malaria

contents

Introduction to Malaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Student Lessons

LESSON 1: Changes in a Long-Term Relationship . . . . . . . . . . . . . 8

LESSON 2: Malaria and Human Diversity . . . . . . . . . . . . . . . . . 21

LESSON 3: Malaria and Population Genetics . . . . . . . . . . . . . . . . 30

LESSON 4: Beyond G6PD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Masters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Credits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

introduction 4

Malaria

introduction to Malaria

Biological evolution is a powerful theory that has tremendous explanatory power for explaining two seemingly contradictory aspects of biological diversity: living species show amazing differences and adaptations to their environment, but they also have many features in common. Unfortunately, many students walk away from AP Biology without a genuine appreciation for evolution, and with an incomplete understanding. The goal of this curriculum unit is to teach students many of the major principles of evolution through the important lens of the coevolution of humans and the malaria parasite.

Overview of the lessons

Lesson 1, Changes in a Long-Term Relationship: In this lesson, students are encouraged to provide their initial ideas about how change over time occurs in living organisms, using the con-text of malaria parasites evolving resistance to an antimalarial drug. Students then learn about four historical explanations for change over time, and they compare their initial ideas to the historical ideas. Students then investigate the results from six different experiments, and they use the results to build an explanation for change over time based on natural selection.

Lesson 2, Malaria and Human Diversity: Students strengthen their ability to develop explana-tions with natural selection by using human diversity in response to coevolution with malaria as the context in Lesson 2. The lesson begins with an investigation of why certain individuals react poorly to taking a specific antimalarial drug. Through this investigation, students learn about G6PD deficiency, the most common enzyme deficiency among humans. Students then use evidence from four experiments and data sets to construct an argument that natural selection has shaped patterns of G6PD diversity in humans.

Lesson 3, Malaria and Population Genetics: Students learn how to use the Hardy-Weinberg equilibrium model to make predictions about populations in the future and how biologists use an understanding of the model to better understand how populations are changing over time. Stu-dents apply their understanding of the Hardy-Weinberg equilibrium model to problems related to the coevolution of humans and the malaria parasite. Students then use a population genetics simu-lation to conduct and analyze an investigation on an evolutionary question of their choosing. In the process, students learn about genetic drift, another important evolutionary mechanism.

Lesson 4, Beyond G6PD: In Lesson 4, students apply what they learned about evolution to explain patterns of diversity in other human genes whose allele frequencies have also changed in response to malaria. Students complete a summative assessment as they work in teams to develop a scientific summary report or creative presentation describing how malaria has shaped the frequency of alleles for at least one more gene.

introduction 5

Malaria

Table T1. Summary of AP Biology essential knowledge and learning objectives.

Lesson AP Biology essential knowledge AP Biology learning objectives

Lesson 1: Changes in a

Long-Term Relationship

1.A.1 a–e; 1.A.2 a–d; 1.A.4 a–b;

1.C.3 a–b

1.2, 1.4, 1.5, 1.9, 1.11, 1.25, 1.26

Lesson 2: Malaria and Human

Diversity

1.A.1 a–e; 1.A.2 a–d; 1.A.4 a–b;

1.B.1 a; 1.C.3 a–b

1.1, 1.2, 1.4, 1.5, 1.9, 1.10, 1.11, 1.12,

1.13, 1.15, 1.16, 1.25, 1.26

Lesson 3: Malaria and Population

Genetics

1.A.1 a–h; 1.A.2 a–d; 1.A.3 a–b;

1A.4 a–b; 1.C.3 a–b

1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9,

1.10, 1.11, 1.12, 1.13, 1.22, 1.25, 1.26

Lesson 4: Beyond G6PD 1.A.1 a–h; 1.A.2 a–d; 1.A.3 a–b;

1A.4 a–b; 1.C.3 a–b

1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9,

1.10, 1.11, 1.12, 1.13, 1.22, 1.25, 1.26

Source: College Board. (2011). AP Biology curriculum framework 2012–2013. Retrieved from http://media.collegeboard.com/digitalServices/pdf/ap/10b_2727_AP_Biology_CF_WEB_110128.pdf.

Table T2. Suggested timeline based on a 50-minute period.

Timeline Activity

1 week ahead Decide how students will access the websites and simulation used in the lessons.

School Day 1 Lesson 1: Changes in a Long-Term Relationship (50 min)



Lesson 2: Malaria and Human Diversity (40 min)

School Day 4 Lesson 2: Malaria and Human Diversity (15 min)

Lesson 3: Malaria and Population Genetics (35 min)

School Day 5 Lesson 3: Malaria and Population Genetics (50 min)

School Day 6 Lesson 3: Malaria and Population Genetics (50 min)

School Day 7 Lesson 4: Beyond G6PD (15 min to give the assignment; 10 min in a following period to hold a

summary discussion, longer if groups give presentations)

http://media.collegeboard.com/digitalServices/pdf/ap/10b_2727_AP_Biology_CF_WEB_110128.pdf

http://media.collegeboard.com/digitalServices/pdf/ap/10b_2727_AP_Biology_CF_WEB_110128.pdf

introduction 6

Malaria

Table T3. Master materials list.

Lesson Materials and handouts

Lesson 1: Changes in a

Long-Term Relationship

Student handouts

Master 1.2 (1 per student)


Master 1.4 (1 copy for each group of 3)



Other materials

Master 1.1 (project)


Master 1.6 (project or make 1 copy per student)

Access to computer with Internet access

Lesson 2: Malaria and Human

Diversity

Student handouts




Other materials



Lesson 3: Malaria and

Population Genetics

Student handouts

Master 3.2 (1 per student if not handed out in Lesson 2)


Other materials



50 marbles of one color (or other similar object)

50 marbles of a second color

Opaque container to hold the marbles

Student access to computers with Internet access (1 for each student pair;

1 for the teacher)

Chart paper (optional)

Lesson 4: Beyond G6PD Student handouts


Master 4.2 (Each group gets 1 of the 5 allele data sets.)

Other materials

Access to a computer with Internet access (1 for each student pair;

1 for the teacher [optional])

Different-colored pens or pencils

Presentation materials (optional)

introduction 7

Malaria

Background information about Malaria

A useful summary of background material on malaria is available at the Centers for Disease Control and Prevention’s “Malaria” web page, http://www.cdc.gov/MALARIA/.

Students may benefit from using the National Genome Research Institute’s “Talking Glossary of Genetic Terms,” http://www.genome.gov/Glossary.

http://www.cdc.gov/MALARIA/

http://www.genome.gov/Glossary

Malarialesson 1: changes in a long-term relationship

8

l e s s O n 1

changes in a long-term relationship

lesson summary

Brief DescriptionThe main goal for this lesson is for students to express their personal, initial ideas about mecha-nisms for change over time and to compare their ideas with four different historical explanations for change over time. One of the essential features of constructivist teaching is to ask learners to record and make explicit their initial ideas. Teachers should then lead students through engaging and interesting experiences that help them reflect and improve their understanding. In this lesson, students are first introduced to the vast impact that malaria has had on human health. They then are asked to record their ideas about how the malaria parasite has changed over time. Students then explore and analyze the results of six different experiments and use the results to build an explana-tion for change based on natural selection.

ObjectivesAfter completing this lesson, students will

• understandthetremendousimpactofmalariaonhumanhealth,• recognizemajorexplanationsthathumanshavedevelopedforchangeovertime

and how their initial explanations fit within these categories,• usedataandevidencetomakeclaimsthatrelatetonaturalselection,• revisetheirinitialexplanationsforchangebasedontheirnewunderstandings,and• begintoappreciatethevalueofunderstandingevolution.

Teacher Preparation

Materials and HandoutsStudent HandoutsMaster 1.2 (1 per student)Master 1.3 (1 per student)Master 1.4 (1 copy for each group of 3)Master 1.7 (1 copy for each group of 3)Master 1.8 (1 per student)


9

Other MaterialsMaster 1.1 (project)Master 1.5 (project)Master 1.6 (project or make 1 copy per student)Access to computer with Internet access

Preparation InstructionsThe best preparation for the unit as a whole is to anticipate any roadblocks you may encounter from students. A working understanding of Mendelian inheritance and common genetics terminol-ogy will benefit students as they work through this unit. Also, knowing your students is invaluable when introducing a set of concepts that some may find difficult to reconcile with their worldviews. Prepare yourself to create an environment in which students know and feel that their worldviews are respected, yet keep a major focus on the nature of scientific knowledge. Review the optional Cultural and Religious Sensitivity (CRS) Teaching Strategies Resource that is a part of the Teaching Evolution through Human Examples project (available as a separate document) and decide if you want to use it before beginning this unit.

Download the Howard Hughes Medical Institute (HHMI) video titled Malaria: Human Host, on the life cycle of malaria, at http://www.biointeractive.org/malaria-human-host. Download only the Human Host video, in the format that best works with your computer. If you choose to show the optional video Herbs and Empires: A Brief, Animated History of Malaria Drugs in Step 18, make sure you can access the NPR website, http://www.npr.org/blogs/health/2012/12/13/167188333/herbs-and-empires-a-brief-animated-history-of-malaria-drugs, on your school computer.

If you are using the student workbooks, you may want to wait to hand out the pages that corre-spond to Master 1.7. On Master 1.6, students make predictions about the experiments described in Master 1.7.

Procedure

Estimated time: 2 50-minute periods, 10 minutes on Day 3

Note: The pedagogical approach in this curriculum unit asks students to construct an understand-ing of evolution over the series of lessons, building from specific examples to general principles (an inductive approach). A crucial practice to help students develop their own understanding is to have students reflect on their understanding over time (i.e., engage in metacognition). One power-ful approach to support metacognitive habits is for students to record their ideas in a notebook or scientific journal. To help with this purpose and to help students organize the handouts from this unit, consider using the student workbook that accompanies this unit.

http://www.biointeractive.org/malaria-human-host

http://www.npr.org/blogs/health/2012/12/13/167188333/herbs-and-empires-a-brief-animated-history-of-malaria-drugs



10

lesson 1, day 1 z z z

1. Begin the lesson by explaining to students that for the next week or so they will develop scientific arguments and explanations to help them better understand how a major disease throughout human history has affected humans and other species. In the process, they will learn to apply the “big ideas” from the most powerful theory in biology, biological evolution.

It is important to set a tone of student empowerment as you begin this unit to encourage a high level of intrinsic motivation. Convey that everyone develops explanations as they go through life, but learning to think critically and use logic and evidence in developing explanations will serve them well, no matter what course their lives take. Developing stronger abilities to construct scientific explanations requires coaching and practice. Many students resonate with the idea that they will construct their own valid conclusions based on evidence, as opposed to being told how to think.

2. Give students one minute to work in groups of three to come up with a list of what they think are the top three causes of death in human history.

3. Ask three or four groups to share their top few responses and ask them to briefly articulate their reasoning. After a short discussion, reveal that some scientists sug-gest that malaria is the leading cause of death in human history. In fact, some estimates suggest that 1 out of every 2 people who have ever lived have died due to complications from malaria. Tell students that in this unit they will explore how sci-entists and health workers use explanations based on evolution to better understand this terrible disease.

Students in the United States may not understand how large an influence infectious dis-eases have had on human health throughout history, and still have today in many low-in-come countries. The World Health Organization (2014) suggests that, in 2012, malaria was the sixth-leading cause of death in low-income countries and infectious diseases were 4 of the top 6 causes. In high-income countries, the leading causes of death were, in order, heart disease, stroke, lung cancers, and Alzheimer’s and other dementias.

For more information, visit the World Health Organization’s website at http://www.who.int/mediacentre/factsheets/fs310/en/index.html.

4. Share the following facts from the Centers for Disease Control and Prevention (2015) about malaria as a worldwide health problem.

• “3.4billionpeopleliveinareasatriskofmalariatransmissionin106countries and territories.”

http://www.who.int/mediacentre/factsheets/fs310/en/index.html



11

• “TheWorldHealthOrganizationestimatesthatin2013malariacaused198 million clinical episodes, and 500,000 deaths.”

• “Anestimated91%ofdeathsin2010wereintheAfricanRegion,fol-lowedbytheSouth-EastAsianRegion(6%),andtheEasternMediterra-neanRegion(3%).About86%ofdeathsgloballywereinchildren.”

For more information, visit the Centers for Disease Control and Prevention’s website at http://www.cdc.gov/malaria/about/facts.html.

5. Project Master 1.1 showing where malaria is found across the world. Note that this image needs to be shown in color. Highlight that although malaria is not currently a problem in many high-income countries, malaria is still a major concern. Malaria affects a larger number of people and is even more difficult to treat compared to even a generation ago. Then ask students to copy the following focus question into theirnotebooks:“Whatisascientificexplanationforwhymanymalariaparasitesare resistant to antimalarial drugs?”

6. Give each student a copy of Master 1.2 and ask students to read the introduction and questions. Show students the four-minute HHMI video on the life cycle of the parasite that causes malaria in the human host. As students watch the video, ask themtotakenotessummarizingtheparasite’slifecycle.Studentscanusetheirnotestoanswerthequestionsonthemaster.Reviewtheanswerswithstudents.

The Malaria: Human Host video is available at HHMI’s BioInteractive website, http://www.biointeractive.org/malaria-human-host.

z z z

answer Key for Questions on Master 1.2

1. How does the malaria parasite move from the mosquitoes to humans?

The parasite moves into humans through the bite of a female mosquito. Students may be interested

to learn that approximately 20 parasites are typically transferred, though malaria can develop from

the transfer of only one individual.

2. After entering the circulatory system, in what organ does the malaria parasite reside?

The parasite initially moves into cells in the liver.

http://www.cdc.gov/malaria/about/facts.html




12

3. What cellular process takes place in the malaria parasite once it is inside the liver?

The parasite undergoes the process of mitosis to create thousands of new nuclei and

eventually new cells.

4. How many offspring can one parasite make in one liver cell?

In just one infected liver cell, thousands of new parasite individuals can form.

5. Where does the parasite move after leaving the liver?

The parasite moves back into the circulatory system and enters red blood cells.

6. What does the parasite do inside red blood cells?

The parasite undergoes more rounds of reproduction. Students may be interested in the further

detail that in two days, one parasitic cell produces from 8 to 24 daughter cells. These cells are

released into the blood when the red blood cell ruptures, and each can infect more red blood cells.

7. What are the effects of malaria?

The effects are fever, loss of blood, convulsions, brain damage, and coma.

8. What percentage of people are likely to contract malaria each year?

Ten percent of people worldwide will be affected by malaria each year.

9. Who dies from malaria?

Fatalities from malaria mostly occur among pregnant women and children under five years old.

10. Over a period of two weeks, how many new parasite individuals could be formed starting with

just one parasitic cell inside a human? Use the following information to solve the problem.

•Initialinfectionofalivercell:Infectionlastssixdays,andupto40,000individualsareformed.

•Redbloodcellinfection:Everytwodays,eachparasiticcellcanmakeupto24newindividuals.

Over six days, 40,000 new individuals are formed. In the remaining eight days, four rounds of repro-

duction can take place in red blood cells, with each round producing 24 new individuals. The total

number is then 40,000 × 244 = 13,271,040,000 individuals.

z z z


13

7. Explain to students that controlling malaria has been and remains a major focus in world health. They will now explore some of the history of malaria control efforts and work to explain the results. Give each student a copy of Master 1.3. Ask stu-dents to read the information and then use their prior knowledge to answer the questionattheend.Reassurethemthattheywillrevisitandimprovetheirexpla-nations in future lessons. Their focus should be on articulating their thinking and using logic and reasoning in their articulations.

Do not impose a particular format or any special components on the initial explanations that students develop. But make sure that students put their initial answers in a distinct place in their student notebooks, surrounded by a lot of white space. Some students may be uncomfortable that all their questions are not resolved at this point.

You may want to put a strong emphasis on why developing accurate explanations for why certain malaria control efforts have suffered setbacks is so critical. Millions of lives are shortened or fundamentally changed when antimalarial drugs fail.

8. Tell students that they made an initial explanation for change over time in popu-lations of the malaria parasite. They will now learn about four general classes of explanations for change over time. Give each group of three students a copy of Mas-ter 1.4. Ask the class to read the introduction and then complete Task 1.

As groups are working to complete Task 1, walk among the students and listen to their ideas for bumper stickers for each explanation type. Encourage groups with especially good examples to share their ideas in the class discussion.

The four explanation types provided are based on common explanations offered for change over time uncovered through cognitive research. Explanation 1 is called an essen-tialist bias, Explanation 2 is Lamarckian reasoning, and Explanation 3 may show a teleo-logical bias (features exist for a purpose, based on need) or an intentionality bias (changes are directed by an agent or intelligence; an organism “realizes” it should change).

If students are already well steeped in evolution, they may be confused as to why they are learning about alternative explanations that are not correct. Justify this approach to students by explaining that the three alternative explanations provided are very common and in some ways represent default modes of thinking. They are also the explanations that predominated for most of human history. As students develop as professionals in their fields of choice, it is important for them to recognize common patterns in people’s thinking.


14

The pedagogical approach helps students reflect on their own initial explanations before engaging with evidence. There is some support from the evolution education research that this approach helps students develop a better understanding of natural selection.

Students may wonder why “important” traits are highlighted in Explanation 1. Of course, it is difficult to determine which traits are important, making “essential” traits difficult to define. Certainly, if traits affect survival or reproduction, they should be con-sidered important. An essentialist explanation suggests that these changes do not occur. Also recognize that if some traits can change within a population (microevolution), then some changes in different populations may affect the ability of those populations to interbreed, which may lead to speciation (macroevolution).

9. Debrief Task 1 by asking groups to volunteer their bumper stickers for each type of explanation. Capture at least two bumper stickers for each explanation and display them throughout the classroom for the remainder of the unit.

As the lessons proceed, refer to the bumper stickers when you hear students offering alternative explanations and encourage students to reference them in their discussions with each other.

10. Ask students to work together to complete Task 2. Give students only about 10 min-utes to complete their work.

Students may struggle to develop an answer for each explanation type. Ask them not to dwell on every detail at this point. Reassure them that they will compare their answers to “expert” answers soon.

11. Project Master 1.5 and ask groups to briefly compare and contrast their answers to those provided on the master.

Some students may wonder why they worked as a group to develop their answers only to find out the “answer” in the next step. Reinforce the notion that the role of a teacher is to help students learn to think for themselves. Learning to practice developing their own ideas and then comparing their thoughts to those of experts will better help them with this essential scientific practice than simply being told initially what experts think.

12. Encourage students to find and share examples of each type of explanation outside of class.

Educational research suggests that activities such as the one described in this step help make learning about evolution more relevant to high school students.


15

13. Tell students that for homework they will consider a range of different experiments that will help them develop an explanation for the process that led to the develop-ment of resistance to chloroquine (CQ) in Plasmodium falciparum. Their task is to read through the research in each experiment on Master 1.6 and to make a pre-diction, using the logic from each of the four types of explanations. They should also describe their own predictions. Project Master 1.6 or hand out a copy to each student.

If you are using the student workbooks, you may want to wait to hand out the pages that correspond to Master 1.7, as these have the actual results for the experiments described on Master 1.6.

If you have time, there are benefits to letting students begin the homework assignment in class.

If you have evidence that a large fraction of your students readily accept explanations based on natural selection, consider just asking them to make their own predictions. If you choose this route, you may also want to give students a copy of Master 1.6 for them to analyze as homework, after they have finished with their own predictions (and skip to Step 15 the next day).


14. Hold a short debriefing session on the predictions for each of the six experiments, which use the logic from the four different types of explanations.

Suggested predictions for each of the experiments follow.

z z z

answer Key for Tasks on Master 1.6

experiment 1

Explanation 1: Answers may vary. Some students might suggest that the ability to survive a poison is

a fundamental change, so variation should not exist. Others could argue that this variation is not

essential if CQ is not present, so it may exist.

Explanations 2 and 3: There may be variation among the individuals, but the variation will not be

genetic. Students will learn about this relationship in later experiments.

Explanation 4: One would predict that some individuals will be resistant to CQ and some will not.

Students will see from future experiments that there is a genetic basis for this resistance.


16

experiment 2

Explanation 1: DNA is essential for organisms, so one might expect there to be very little to no varia-

tion in the DNA sequences among the individuals.

Explanations 2 and 3: There may be variation among the sequences, but the variation will not be

related to the ability to resist CQ. Students will learn about this relationship in later experiments.

Explanation 4: One would predict a large amount of variation in the DNA sequences among all the

individuals.

experiment 3

Explanation 1: Proteins and the DNA that codes for proteins are essential for organisms, so one might

expect there to be very little to no variation in the protein sequences among the individuals.

Explanations 2 and 3: There may be variation among the sequences, but the variation will not be

related to the ability to resist CQ.

Explanation 4: One would predict a variation in the proteins among all the individuals and that the

variation will be related to the ability to resist CQ.

experiment 4

Explanations 1, 2, and 3: One would not expect a change in resistance if the pfcrt allele was moved

between strains.

Explanation 4: One would predict that the movement of the pfcrt allele from a resistant strain into a

susceptible strain would cause the susceptible strain to become resistant.

experiment 5

Explanations 1, 2, and 3: No difference in the frequency of pfcrt alleles would be expected.

Explanation 4: One would predict a higher frequency of the pfcrt allele that causes resistance to

CQ in areas with high CQ use.

experiment 6

Explanations 1, 2, and 3: No difference in the frequency of pfcrt alleles would be expected.

Explanation 4: One would predict the frequency of the pfcrt allele to decrease over time as

CQ use was discontinued if the mutant allele lowered fitness without the CQ present.

z z z

15. Tell the class that it will now examine the results from the six experiments. Give each group of three a copy of Master 1.7. Tell them to examine the results one experiment at a time. Debrief the results after groups finish the tasks with each experiment.


17

z z z

answer Key for Tasks on Master 1.7

experiment 1

1. Usetheevidencetomakeaclaimthatanswersthequestion,“Doesvariationexistamong

Plasmodium falciparum individuals for resistance to CQ?” Make sure to refer to the evidence.

The fact that some individuals are resistant to CQ and some are not, even in the same population,

is evidence that there is variation among individuals.

experiment 2

2. Usetheevidencetomakeaclaimthatanswersthequestion,“DoesvariationinDNAexist

among individual parasites?” Make sure to refer to the evidence.

The results show that there is a great diversity in the DNA sequences from different individual

parasites.

experiment 3

3. Use the data in Table 1 to make a claim that answers the focus question, “Are specific variations

inPfCRTproteinsassociatedwithCQresistance?”

The results show that specific sequences of amino acids in the PfCRT protein are associated

with CQ resistance. Interestingly, the samples from South America show a different pattern from

the samples in Asia and elsewhere, indicating that the parasites in South America independently

evolved resistance. In fact, resistance has evolved at least six times independently.

experiment 4

4. Make a claim that answers the focus question, “Does changing one allele in the parasite affect

its resistance to CQ?” Use the appropriate evidence in your claim.

The data suggest that inserting the pfcrt allele does confer resistance to CQ to a strain that was

previously susceptible.

experiment 5

5. Use the data to make a claim about the frequency of the allele that causes CQ resistance in

different regions.

The data show that the frequency of the pfcrt allele is much higher in geographic areas that have a

high amount of malaria. The data suggest that the allele frequency for pfcrt changes in P. falciparum

populations as the environment for the parasites changes over geographic space.


18

experiment 6

6. Use the data to make a claim about the frequency of the allele that causes CQ resistance when

the environment for the parasite changes.

The data suggest that the allele frequency for pfcrt changes in P. falciparum populations as the

environment for the parasites changes over time. These results raise the interesting question of why

the K76T allele frequency decreased in Malawi. In other words, when CQ use stopped, why didn’t

the frequency of the resistant genotype remain constant? What selection force might account for

this? The data suggest that the resistance mutation entails costs for the parasite when CQ is not

present. These costs may be metabolic, but they certainly influence survival and/or reproduction. In

an environment with CQ, however, the benefits of the resistance mutation outweigh the costs. Use

this example to reinforce the critical concept that natural selection is highly dependent on context

and that the results of the process of natural selection are a compromise of costs and benefits of the

process, but they are not leading to perfection.

Education research suggests that students have difficulty understanding the loss of a trait through

natural selection. You may want to emphasize to students that this is an example of the loss of a

specific trait.

z z z

16. Ask students to revisit the answers they gave to the question on Master 1.3 in Step 7. Ask them to revise their answers based on their new understandings by creating a tableintheirnotebookstosummarizetheevidencefornaturalselectioninP. fal-ciparum. Their tables should have the following rows: “Variation,” “Inheritance,” “Selection,” and “Adaptation.”

Summarize for students that a wide range of experiments and a broad range of different types of data support explanations based on natural selection. Table T4 is a summary of how the evidence from the experiments with P. falciparum support an explanation based on natural selection.


19

z z z

answer Key for step 16

Table T4. Summary of evidence for natural selection in P. falciparum.

Aspect of natural

selectionEvidence/inference

Variation In Experiment 1, the data show that variation exists for CQ resistance (some individu-

als are resistant, and some are not).

Inheritance One form of an allele of the pfcrt gene codes for a protein that is associated with CQ

resistance. Evidence from Experiments 3 and 4 support this claim. Additional support

is provided by the results from Experiment 2.

Selection If a parasite has a specific allele for the PfCRT protein, it can survive in higher

concentrations of CQ, which leads to increased fitness. Evidence from Experiment 4

supports this claim.

Adaptation Evidence from Experiment 5 shows that if CQ use is high, so is the frequency of the

K76T allele, which confers resistance to the parasite. Similarly, Experiment 6 shows

that if the selective environment changes and CQ use is low, the frequency of the

K76T allele decreases over time.

z z z

17. Give students one copy each of Master 1.8 and ask them to complete the analysis questions for homework.

If you have time, there are benefits to letting students begin the homework assignment in class.


18. Reviewstudents’answerstotheanalysisquestionsfromthepreviousday.

The questions ask students to apply their understandings to new scenarios. It is import-ant to give them time to review and revise their answers.


20

z z z

answer Key for analysis Questions on Master 1.8

1. Compare and contrast the evolution of resistance to chloroquine (CQ) in Plasmodium falciparum

to resistance to antibiotics in bacteria.

Students should recognize that the process by which resistance evolves in both P. falciparum and

bacteria is the same. They may note that the life cycle of P. falciparum is more complex and involves

sexual reproduction, which affects the amount of genetic diversity in P. falciparum populations.

2. TheHIVvirusveryquicklyevolvedresistancetosomeofthefirstmedicinesdevelopedtotreat

AIDS.Usinganunderstandingofevolution,healthprofessionalsdevelopedanewtreatmentpro-

tocolforpeoplewithHIVcalledhighlyactiveantiretroviraltherapy(HAART).Thistherapyinvolves

administering three or more drugs to a patient at once to help avoid the evolution of resistance.

With this in mind, suggest an approach for treating people with malaria that may help counter

the evolution of resistance to CQ.

Students will likely suggest that malaria should be treated using a combination of drugs.

In fact, a common approach for treating malaria is called artemisinin-based combina-

tion therapy (ACT). You may want to direct students to the NPR video Herbs and Empires:

A Brief, Animated History of Malaria Drugs, available online, to get a brief introduc-

tion to treatments for malaria: http://www.npr.org/blogs/health/2012/12/13/167188333/

herbs-and-empires-a-brief-animated-history-of-malaria-drugs.

3. The parasite P. falciparum shows a great deal of diversity. Use this information to make a predic-

tion about the ease or difficulty in developing a vaccine for malaria.

The vast amount of diversity in P. falciparum has unfortunately frustrated all attempts to develop an

effective vaccine for widespread use.

z z z



Malarialesson 2: Malaria and human diversity

21

l e s s O n 2

Malaria and human diversity

lesson summary

Brief DescriptionThe major goal of the lesson is to help students deepen their understanding of natural selection as they examine how deaths due to malaria may have affected the frequency of certain alleles of the G6PD gene in humans. Students begin by investigating why certain individuals react poorly to tak-ing antimalarial drugs. Eventually, they learn about G6PD deficiency, the most common enzyme deficiency among humans. Students then explore four data sets, which they use to construct an argument that natural selection has shaped patterns of G6PD diversity in humans.


• understandthetremendousimpactofmalariaonhumanhealth,• interpretdatathathelpedmedicalprofessionalsunderstandahealthmystery,• usedataandevidencetodevelopanargumentthatnaturalselectionhasshaped

human diversity, • revisetheirinitialexplanationsforchangebasedontheirnewunderstandings,and• betterappreciatethevalueofunderstandingevolution.

Teacher Preparation

Materials and HandoutsStudent HandoutsMaster 2.1 (1 copy for each group of 2)Master 2.3 (1 copy for each group of 3)Master 3.2 (1 per student)Other MaterialsMaster 2.2 (project)Master 2.4 (project)

Preparation InstructionsIn this lesson, students get further practice developing an argument based on data for natural selec-tion. Aside from making the appropriate copies, no additional preparation is required.


22

Procedure

Estimated time: 40 minutes on Day 3, 15 minutes on Day 4

Note: This lesson picks up after students review their homework from Lesson 1.


1. Tell students that in the previous lesson, they learned how the antimalarial drug chloroquine (CQ) has become much less effective due to evolution of the parasite. In this lesson, they will learn about new approaches to try to eradicate malaria that rely on a different set of medicines. One important drug in this effort is called primaquine. Unfortunately, some people cannot take this important drug, and the reason, interestingly, has a lot to do with how the malaria parasite has shaped and affected diversity in humans. In other words, the malaria parasite and humans are coevolving. Students will investigate this medical problem in this lesson.

This introduction helps drive home the practical benefits of better understanding the coevolution of humans and malaria parasites.

2. Ask students to form groups of two to work through how health professionals inves-tigated the mystery of why certain people cannot take the drug primaquine. Give each group of two a copy of Master 2.1.

Many students find the challenge of solving health problems motivating.

3. As you interact with groups completing Master 2.1, decide if you need to debrief the answers with the class after each section or if you can wait until they all have finished.

It is preferable to wait until the groups have attempted all five analysis questions, but if you notice groups struggling, then hold the debriefing sessions sooner rather than later.

z z z


1. Threeprimarycausesofdiseaseareinfectionbypathogens,geneticeffects,orexposuretotox-

insorotherextrinsicfactorsfoundintheenvironment.Useevidencefromthereadingtopredict

the cause of the condition that made some people react poorly to the drug.

The reaction to primaquine mostly occurred within one ethnic group (West Indian migrants of African

descent), which should lead students to suspect that the reaction has a genetic basis. This evidence

alone is not conclusive, however.


23

2. Describe the data you would like to collect to further test the prediction you made in the previ-

ous question.

Be open to a wide range of logical responses given students’ prior experience with genetics. Stu-

dents may suggest they would like to examine pedigrees showing patterns of susceptibility to the

condition through generations. They may also suggest they would like to get data on whether or not

specific genes are associated with the condition. Students will access both of these types of data

later in the lesson.

3. UsethedatainFigures1and2tomakeaclaimaboutwhetherthetoxicityofthedrugpri-

maquinewasduetothedrugbeinggenerallytoxictosomepeopleoriftherewassomething

different in some people’s red blood cells that caused them to react to the drug.

Data from the first experiment suggest that the red blood cells from primaquine-sensitive individuals

were rapidly degraded if primaquine was present. Data from the second experiment further support

the hypothesis that people who are sensitive to primaquine have a functional difference in their red

blood cells.

4. ThedatainFigures1and2camefromresearchdoneonprisonersintheUnitedStatesduring

WorldWarII.Theprisonersgavetheirfullconsentandvolunteeredfortheirrole.Byparticipating,

they could receive reduced sentences. This type of research is forbidden today. What ethical

issues arise for you in this situation?

Students might note that the prisoners did give their full consent to participate. Others might argue

that because the prisoners could receive a lighter sentence, they could be subtly coerced into

participating, creating an ethical dilemma. For more information on the use of prisoners in malaria

research, see Comfort, M., (2009), The Prisoner as Model Organism: Malaria Research at State-

ville Penitentiary, Studies in History and Philosophy of Biological and Biomedical Sciences, 40(3),

190–203.

Try to keep the discussion of this question brief, but encourage students to pursue this topic on their

own and bring more information back to a later class. They may also want to keep this topic in mind

for an investigation for a research project in a social studies, history, or other class.

5a. Use Figure 3 to determine the source of electrons to reduce glutathione.

The source of electrons to reduce glutathione is NADPH.


24

5b. IftheenzymeG6PDisimpaired,predictwhatwillhappentotheamountofthereducedformof

glutathione.

If G6PD is not functioning, the amount of NADPH will be low, which will also limit the formation of the

reduced form of glutathione. Both of these factors will make the red blood cells more vulnerable to

damage from oxygen radicals.

z z z

4. Tell students that subsequent research uncovered that G6PD deficiency is quite widespread. Estimates suggest that 400 million people worldwide have the defi-ciency,makingitthemostcommonenzymedeficiencyinhumans(G6PDDefi-ciency Association, 2015). In fact, it affects about 1 in 10 African American males in the United States. A study of US army personnel showed that 12 percent of African American males and 4 percent of African American females were deficient (Chinev-ere et al., 2006). Most of the people who have the deficiency do not show any symp-toms. Scientists have also discovered the gene G6PD, which codes for the G6PD enzyme.CertainallelesoftheG6PD gene cause G6PD deficiency.

If students want more information on G6PD deficiency, they should go to the G6PD Deficiency Association’s website at http://www.g6pd.org and also talk to their own physician.

You may want to reemphasize that most people who are G6PD deficient show no clini-cal symptoms. However, people with this deficiency need to avoid eating fava beans and certain legumes and avoid taking some specific drugs (such as primaquine) or they risk hemolytic anemia.

An interesting historical anecdote is that the Greek mathematician Pythagoras (ca. 580–ca. 500 BCE, of Pythagorean theorem fame) forbade his followers to eat fava beans. One story is that Pythagoras was being pursued by his enemies, but he stopped at a fava bean field, deciding he would rather cast his lot with his enemies than risk poisoning.

5. Project Figure 1 from Master 2.2 to students, which shows the global distribution of G6PD deficiency alleles. Ask students to examine Figure 1, which shows the fre-quency of G6PD deficiency alleles across the globe. Have them exchange ideas with a partner and then write a hypothesis in their notebooks that explains the patterns they observe.

Some students are likely to suggest that the pattern of G6PD deficiency looks similar to the map of malaria frequency they saw in Lesson 1.

http://www.g6pd.org


25

6. Tell students that primaquine is still an important drug in the fight against malaria. Ask, “In what ways would this map be useful to health professionals who want to prescribe primaquine?”

If health professionals know about people’s geographic ancestry, they may be able to make educated inferences about the probability of encountering a person who will have an adverse reaction to primaquine.

7. Project Figure 2 from Master 2.2 to students, which overlays regions with high amounts of malaria onto the global distribution of G6PD deficiency alleles. Ask stu-dents to write a hypothesis in their notebooks that would explain the patterns they observe.Leadaclassdiscussionaboutstudents’answers.

The map leads to the hypothesis that G6PD deficiency may help protect individuals from malaria because G6PD deficiency seems highest in areas that have high amounts of malaria.

If you have the explanation bumper stickers available that students developed in Lesson 1, ask if this map argues against any of the four explanations for change. Help students make the inference that this map argues against the explanation that populations do not change (Explanation 1).

8. Tell students that their next challenge is to develop an explanation based on natural selection for the pattern of G6PD diversity. Ask them to work in groups of three to decide what pieces of evidence they would need to support the hypothesis that human diversity for G6PD has been shaped by natural selection.

You may want to refer students to the description of natural selection (Explanation 4) on Master 1.4.

9. Lead a class discussion to come to a consensus on the types of data that are needed to develop an argument that human diversity for G6PD has been shaped by natu-ralselection.Summarizetheirideasunderfourcolumnsontheboard:“Variation,”“Inheritance,” “Selection,” and “Adaptation.”


26

10. GiveeachgroupofthreestudentsacopyofMaster2.3.Studentsaretoanalyzeeachdata set, answer the accompanying analysis questions with the data, and then use the data to develop an argument that G6PD has been shaped by natural selection. Project Master 2.4 and ask students to use a similar template to help them develop theirarguments.RemindstudentsthattheycanalsouseevidencefromthemapsonMaster 2.2 that you projected.

If you think students may struggle with the somewhat open-ended nature of this task, consider stopping them after they examine Data Set 1. In this data set, students should be able to decipher that G6PD deficiency shows an X-linked pattern of inheritance. Ask, “How do these data fit within an argument for natural selection?” Guide students to recognize that this is evidence that there is variation for G6PD and that this variation is inherited—key components to natural selection. They could then enter this informa-tion into the natural selection template under both “Variation” and “Inheritance.” They should continue with this process for the other data sets.

11. Tell students that they will need to complete their arguments as a homework assign-ment. In the next class session, they will give their arguments to another group to get feedback.

Also tell students that in the next class period, they will use a mathematical model to further investigate the coevolution of humans and the malaria parasite. Give students a copy of Master 3.2 (from the next lesson) to further prepare them for the next day. Ask them to take notes on the main points in the reading.

Use the information in Table T5 to give feedback as you work with individual student groups completing the assignment.

z z z


data set 1

1. UsethedatainthethreepedigreestomakeaclaimaboutthemodeofinheritanceforG6PD

deficiency.

The data in the pedigrees are consistent with an X-linked mode of inheritance.


27

data set 2

2. DotheseadditionaldataconfirmorcontradicttheclaimyoumadewithDataSet1?Explainyour

answer.

The information included in Data Set 2 provides additional confirmation that G6PD deficiency is an

X-linked trait because the causative gene is located on the X chromosome.

data set 3

3. Do you think these alleles came about because people wanted or needed them to come about?

Why or why not?

The alleles came about because of random mutations, not because of need or because an organism

wanted them. This question addresses a common student misconception. You may want to refer

students to the bumper stickers that they developed in Lesson 1.

data set 4

4. “Fitness,” in evolutionary terms, means the relative ability of an individual to survive and repro-

duce.WhatdothedatasuggestabouttheimpactofG6PDdeficiencyallelesonfitnessinareas

that have high rates of malaria?

The data include the implication that G6PD allele A− has a direct impact on survival (and therefore

fitness) as the allele is associated with a major reduction in the risk of severe malaria caused by P.

falciparum. Other data that red blood cells with deficiency alleles inhibit parasite growth indirectly

suggest that the deficiency alleles may affect fitness.

z z z


28

z z z

answer Key for the Template on Master 2.4

Table T5. A summary of the evidence for an argument that patterns of G6PD diversity in humans have been shaped by natural selection.

Aspect of natural


Variation • Maps of G6PD deficiency show that some people have the condition and others do

not. The frequency of the condition varies across the world.

• Pedigrees provide evidence that some family members have G6PD deficiency but

other members do not.

• Medical studies show that there is a wide range of variation for the activity of the

enzyme G6PD.

Inheritance • Pedigrees provide evidence that G6PD deficiency is passed from mothers to sons

(primarily).

• Scientists have identified the gene that codes for G6PD. Its location on the X chro-

mosome is consistent with the patterns on the pedigrees. Numerous alleles that

cause G6PD have been identified.

Selection • Survival and reproduction are needed for evolutionary fitness. If natural selection

has shaped G6PD diversity in humans, some of the alleles for G6PD should affect

survival or reproduction. Direct evidence suggests that people in Africa with the

A− allele have a much-reduced risk of severe malaria.

• Indirect evidence suggests that parasite growth is lower in red blood cells with

deficiency alleles, which likely affects an individual’s survival.

Adaptation • The frequency of alleles for G6PD deficiency varies across populations. For exam-

ple, the A− allele reaches a frequency of 25% in some populations, but it is at 0%

in other populations. Similarly, the Med allele ranges from 2% to 20% in different

populations. These data suggest that the frequency of these alleles has changed in

some populations. The frequency of deficiency alleles is highest in areas that have

high rates of malaria.

z z z

The reading in Master 3.2 is an introduction to the Hardy-Weinberg equilibrium princi-ple or model (H-W model). The term “model” is used to help students link the principle to the critical scientific practice of modeling. You may wish to supplement this reading with a brief reading from your textbook.


29


12. Ask groups to briefly turn and talk with another group about the arguments they developed. Use the following turn-and-talk protocol.

• GroupAreadsitsargumentwordforwordtoGroupB.• GroupBtriestoidentifytheevidenceand/orlogicusedtodevelopthe

argument.• AfterGroupAreads,GroupBsummarizesGroupA’sargumentand

offers feedback on the evidence, logic, and accuracy of the argument.• Groupsthenswitchroles.• Afterbothroundsarecomplete,givestudentsaminutetorevisetheir

arguments based on the feedback they received.

As the students discuss their arguments, walk among them and listen to some of their conversations. This formative assessment will help you gauge how in depth you will need to go in the class debriefing in the next step.

13. Debrief the natural selection argument assignment with the class. Call on different groupstosummarizetheevidenceforeachaspectofnaturalselection.

You may want to point out in the summary the irony in the primaquine-sensitivity scenario. Some people are not able to take a modern medicine to treat malaria because of an enzyme variant that came to be at a high frequency in some groups of people due to evolution in response to malaria.

Malarialesson 3: Malaria and Population genetics

30

l e s s O n 3

Malaria and Population genetics

lesson summary

Brief DescriptionIn this lesson, students learn how to use the Hardy-Weinberg equilibrium model to make predic-tions about populations in the future and how biologists use an understanding of the model to bet-ter understand how populations are changing over time. Students apply their understanding of the H-W model to problems related to the coevolution of the malaria parasite and humans. Students then use a population genetics simulation to conduct and analyze an investigation on an evolution-ary question of their choosing. In the process, students learn about genetic drift, another important evolutionary mechanism.


• usetheirunderstandingoftheHardy-Weinbergequilibriummodeltosolveprob-lems related to the coevolution of the malaria parasite and humans,

• beabletouseapopulationgeneticssimulationtoinvestigateandinterpretevolu-tionary mechanisms such as genetic drift and natural selection, and

• reflectonhowmathematicalmodelsaddtotheevidenceforevolution.

Teacher Preparation

Materials and HandoutsStudent HandoutsMaster 3.2 (1 per student)Master 3.3 (1 per student)Other MaterialsMaster 3.1 (project)Master 3.4 (project)50 marbles of one color (or other similar object)50 marbles of a second colorOpaque container to hold the marbles Student access to computers with Internet access (1 for each student pair; 1 for the teacher)Chart paper (optional)


31

Preparation InstructionsThis lesson uses a population genetics simulation available at the PopG Genetic Simulation Pro-gram website, http://evolution.gs.washington.edu/popgen/popg.html. Please read the copyright information on the web page and then download the appropriate version of the simulation for your computer to your desktop. This procedure will need to be repeated for all the computers available for student use. The lesson is designed so that each group of students can use its own computer. If you do not have that many computers available in the classroom, consider assigning the use of the simulation for homework.

Procedure

Estimated time: 35 minutes on Day 4, 50 minutes on Day 5, 50 minutes on Day 6

Note: Careful timing is needed in this lesson. It is important that students have time to practice completing the Hardy-Weinberg problems and receive feedback. It may be useful to discuss how to solve the problems, then have students complete the practice problems for homework. On the second day, introduce students to the population genetics simulation and have them design their investigations. For homework, students could collect the data for their investigations. On the third day, students could receive feedback on their practice problems and present the results from their investigations.

1. Remindstudentsoftheworktheyhavecompletedsofaranddemonstratehowthelessonsthey’veexperiencedareconnectedbyprojectingthestorylineforthelessonson Master 3.1.

Showing students how the lessons are related reinforces metacognition and helps students recognize the major themes in the lessons.

2. Highlight that in Lesson 3, students will further explore the coevolution of humans and the malaria parasite by learning about a mathematical model and then using simulations based on the mathematical model.

You may want to emphasize that Lessons 1 and 2 primarily referred to clinical or exper-imental data that were obtained directly from individual humans or malaria parasites in different populations. Lesson 3 uses data generated from a scientific/mathematical model. This type of information is also crucial evidence when making scientific explanations. Lesson 3 uses statistical thinking to help students make sense out of evolutionary changes in human populations. Thus, by adding statistical or population thinking to the list of scientific principles from which to draw, students strengthen their ability to explain. Also highlight that in the final lesson, students will apply what they have learned to a different gene in humans that may have been shaped by natural selection.

http://evolution.gs.washington.edu/popgen/popg.html


32

3. If you have not done so already, give each student a copy of Master 3.2 and ask stu-dents to take notes on the main points in the reading.

The reading in Master 3.2 is an introduction to the Hardy-Weinberg equilibrium princi-ple, or model. The term “model” is used to help students link the principle to the critical scientific practice of modeling. You may wish to supplement this reading with a brief reading from your textbook.

4. Call on students to share an important new idea they gained from the reading. ThemajorpointstoemphasizeabouttheH-Wmodelarethatit

• isanullhypothesisasbiologistsexplorewhetherornotpopulationsareevolving,

• allowsbiologiststoestimatethefrequenciesofgenotypesfromthefre-quency of specific alleles,

• involvesfiveassumptions,and• predictsthatgenotypeandallelefrequencieswillnotchangeifalltheas-

sumptionsaretrue.ThislastpointiscalledtheHardy-Weinbergprinciple.

5. TellstudentsthattheywillgainpracticeusingtheH-Wmodeltomakepredictions.Give each student a copy of Master 3.3. Lead students through the information at the beginning of the master and highlight the meaning of different terms and sym-bols. Highlight the difference between allele frequency and genotype frequency.

If your students do not have experience with genetics, you may need to spend some time discussing what an allele is. You may notice that students are given multiple symbols for alleles. Genetics researchers sometimes use dominant and recessive symbols (A, a, respectively) and symbols that do not denote the dominance (A

1, A

2), or sometimes they

may simply use a nucleotide that differs between the alleles (A, G). Having students see and use multiple symbols prepares them for thinking about alleles in different ways, and seeing different representations helps students think more carefully about what an allele actually is. You may want to bring this fact to students’ attention.

6. AskstudentstoworkwithapartnertoreadhowtosolveproblemsusingtheH-Wmodel in which they need to predict the genotypes in the next generation if they are given the frequency of the two alleles. Hold a brief class discussion to clarify any student questions.

Use discussions with student groups to gauge how much time you will need to lead the class discussion about solving these problems. As students work through the step-by-step procedure, they need to solve Step 4 of Situation 1 on their own.


33

z z z

answer Key for situation 1, step 4 on Master 3.3

4. On your own, use the same reasoning to figure out how to calculate the probability of

getting the A2A2 genotype.

The probability of selecting A2 twice = q × q = q2 = (0.43)2 = 0.18 (or 18%).

z z z

7. Depending on the amount of time you have, either have students complete the prac-tice problems in class or for homework. If students complete the problems in class, have them check their work with a partner before discussing the problems as a class.

z z z

answer Key for Practice Problems 1–6 on Master 3.3

1. The researchers mentioned in the sample problem also measured the frequency of the alleles for

the pfcrtgeneinPapuaNewGuinea.ThefrequencyoftheK76Tallelewas0.94.Assumethat

there is only one other allele in the population (which would have a frequency of 0.06). Use the

H-Wmodeltocalculatetheexpectedgenotypefrequenciesinthediploidphaseofthelifecycle

inthenextgeneration.

The frequency of A1A1 = (0.94)2 = 0.88; A1A2 = 2(0.94)(0.06) = 0.11; A2A2 = (0.06)2 = 0.0036.

2. InMalawiin1992,thefrequencyoftheK76TalleleinP. falciparum was 0.85.

a.IftheassumptionsoftheH-Wmodelweretrue,whatfrequencywouldyouexpectforthis

allele in the year 2000? The country stopped using the drug CQ after 1992.

The main conclusion from the H-W model is that if certain assumptions are met, the frequencies

of alleles at a specific gene remain constant from generation to generation. Thus, one would

expect the frequency of the K76T allele to still be at 0.85 in the year 2000.

b.ResearchersmeasuredthefrequencyoftheK76Tallelein2000,anditwas0.13.Which

assumption of the H-W model was most likely not true?

Given that the selective environment for the parasite changed dramatically when the people of

Malawi stopped using CQ, the most likely assumption that was violated was the no selection

assumption.


34

3. G6PDdeficiencyinhumansisanX-linkedtrait,andtheH-Wmodelcanbeadjustedtoanalyze

X-linkedtraits.However,topracticeusingtheH-Wmodel,let’sassumethatitfunctionslikean

autosome.InsomehumanpopulationsinAfrica,thefrequencyoftheA− allele is 0.25. You

exploredthisalleleinLesson2.Assumethereisonlyoneotheralleleinthispopulation(fre-

quency=0.75).UsetheH-Wmodeltocalculatetheexpectedgenotypefrequenciesinthenext

generation.

In this problem, let A1 = the A− allele and A2 = the alternative allele. A1A1 = (0.25)2 = 0.063;

A1A2 = 2(0.75)(0.25) = 0.38; A2A2 = (0.75)2 = 0.56.

4a. Calculatetheexpectedgenotypefrequenciesforthenextgeneration.

The expected frequency of GG = (0.8)2 = 0.64; Gg = 2(0.8)(0.2) = 0.32; gg = (0.2)2 = 0.04.

4b. Supposeyoumeasuredthefrequencyofeachgenotypeandfoundthefollowingresults:

GG = 0.50, Gg = 0.40, gg=0.10.Howcouldyouexplaintheseresults?

There are fewer homozygous dominant genotypes than expected, and more homozygous reces-

sive genotypes. One of the assumptions of the H-W model must not be true. In this case, stu-

dents learned in the previous lesson that the A− allele affects fitness, so selection is likely to help

explain the results. Recent studies suggest that the A− allele in a region with high rates of malaria

has a strong effect on fitness, giving individuals a 25 percent fitness advantage. This level is one

of the strongest impacts on fitness of any allele in humans.

5. The frequency of the A−alleleinnorthernEuropeansisverylowcomparedtothefrequencyin

someAfricans.However,thevastmajorityofallelesforgenesstudiedinEuropeansandAfricans

are similar. One gene in both groups has two alleles. The frequency of allele 1 was 0.76 and of

allele2was0.24.UsetheH-Wmodeltocalculatetheexpectedgenotypefrequenciesinthe

nextgeneration.

The frequency of A1A1 = (0.76)2 = 0.58; A1A2 = 2(0.76)(0.24) = 0.36; A2A2 = (0.24)2 = 0.06.

6. WhatdoyouthinkitmeansthatEuropeansandAfricanshaveverysimilarallelefrequenciesfor

most genes?

The similarity in gene frequencies suggests that the two groups are closely related. Make the

general but critical point that all humans are very closely related. There is more genetic variation

within human populations than among populations.

z z z


35

8. Ask students to work with a partner to solve problems when they are given a table of genotypes. Hold a brief class discussion to clarify any student questions.

As students work through the step-by-step procedure, they need to solve part of Step 2 of Situation 2 on their own.

z z z

answer Key for situation 2, step 2 on Master 3.3

2. Calculate the genotype frequencies.

frequency of A1A1 = frequency of AA = 7/10 total = 0.7

frequency of A1A2 = frequency of AS = _2/10 = 0.2

frequency of A2A2 = frequency of SS = _1/10 = 0.1

z z z

9. Again, depending on the amount of time you have, have students either complete the practice problems in class or for homework.

z z z

answer Key for Practice Problem 7 on Master 3.3

Note:Theseexamplesarebasedonempiricalestimatesforoneoftheallelesinvolvedinthe

evolutionoflactosetolerance.Inreality,however,therearemanymorethantwoallelesforthis

locus.

7a. Use the data in Tables 2 and 3 to calculate the allele and genotype frequencies of the

two populations.

For southern Europeans, the frequency of AA = 1/10 = 0.1; Aa = 3/10 = 0.3; aa = 6/10 = 0.6.

The frequency of A = 5/20 = 0.25, a = 15/20 = 0.75.

For northern Europeans, the frequency of AA = 6/10 = 0.6; Aa = 3/10 = 0.3; aa = 1/10 = 0.1.

The frequency of A = 15/20 = 0.75, a = 5/20 = 0.25.

7b. Predictthegenotypefrequenciesofthenextgeneration.

The prediction for southern Europeans in the next generation is AA = (0.25)2 = 0.06;

Aa = 2(0.25)(0.75) = 0.38; aa = (0.75)2 = 0.56.


36

The prediction for northern Europe in the next generation is AA = (0.75)2 = 0.56; Aa = 2(0.25)(0.75) =

0.38; aa = (0.25)2 = 0.06.

7c. Describe your ideas for why the allele frequencies are different in each group.

Students should recognize that different allele frequencies for these alleles in two

groups that are otherwise closely related suggest that one of the mechanisms of evo-

lution has caused the change. In this case, biologists have a range of evidence that

suggests that natural selection is the major cause of this change in allele frequencies.

z z z

Note: Most AP Biology textbooks have Hardy-Weinberg equilibrium problems. Consider assign-ing these additional problems to help students apply the concepts to examples outside of humans. You may also want to assign more problems that relate to sickle cell disease. The Howard Hughes Medical Institute’s BioInteractive website has a useful set of problems (“Population Genetics, Selection, and Evolution”) at http://www.hhmi.org/biointeractive/population-genetics-selec-tion-and-evolution (download the items by clicking on Student Handout or Teacher Materials on the right-hand side).


Note: Depending on how you structured the previous day, you may need to begin Day 5 by reviewing student homework problems from Master 3.3.

10. TellstudentsthatscientistsusethemathematicsbehindtheH-Wmodeltofurtherdevelop models and simulations to investigate and make predictions about evolu-tion. Students will use the simulation to investigate questions about evolution of their own design.

If you would like students to gain practice developing a spreadsheet model of the H-W model, consider implementing Lab 2 from the AP Biology lab manual. This additional activity would add at least one additional class period to this activity.

11. Open the PopG Population Genetic Simulation and project the opening page to students. Point out that in this simulation, students will monitor the frequency of one allele (A) in a gene that has two alleles (A and a) in a population over time. The y-axis shows the frequency of the A allele. The x-axis shows generations.

http://www.hhmi.org/biointeractive/population-genetics-selection-and-evolution

http://www.hhmi.org/biointeractive/population-genetics-selection-and-evolution


37

As stated in the introduction, this lesson uses the PopG Genetic Simulation Program available at http://evolution.gs.washington.edu/popgen/popg.html. Veteran teachers sug-gest that many students have difficulty understanding the meaning of the y-axis in these types of simulations. You may want to remind students that the symbol they used for the frequency of the A allele was p.

12. Click on Run, then New Run to see the variables that students can change in the simulation.ProjectMaster3.4andsummarizethevariablesthatcanchangeinthemodel. Ask students how the variables that can change relate to the assumptions of theH-Wmodel.

Students should recognize that the simulation allows them to investigate four of the five assumptions in the H-W model (all except random mating).

13. Before using the simulation, introduce students to genetic drift with the following demonstration.

• Showstudents50marblesofonecolorandtellthemthatthemarblesrepresent allele A

1. Then show them 50 marbles of another color, which

represent a second allele (A2).

• AskstudentsforthefrequencyofA1(50/100=0.5).

• Putthemarblesintotheopaquecontainer.Let10studentseachpickout a marble, and then recalculate the frequency of allele A

1. Fill the

container with the appropriate number of marbles of each color, accord-ingtothenewfrequency.Repeatthisprocedureafewtimes.

• Tellstudentsthatgeneticdriftistherandomchangesinallelefrequen-cies over time due to chance or sampling. It is another mechanism of evolution.

• Showstudentshowyoucouldusethesimulationtoshowthesameresults as the demonstration. Set Population Size=10,Generations to run=5,andNumber of populations evolving simultaneously=1.Projectthe results of the simulation. Ask students to sketch the results in their notebooks and to write a brief description of what the data mean.

As students write their descriptions of the results, walk among the groups to make sure they are interpreting the results correctly.

14. Tell students that they will collect data to answer the following question as a class: “Could the high frequency (25 percent) of the A− allele for the gene G6PD in some groups of people living in sub-Saharan Africa have been caused by genetic drift instead of natural selection?”



38

15. Lead a class discussion about how to set up the simulation to test this scenario. Use Table T6 as your guide.

Table T6. Variable settings to address the question in Step 14.

Variable Comments

Population size The simulation should start with a maximum population size (10,000), but other

reasonable sizes should be tried, too (greater than 500).

Fitness of the 3

genotypes

Under a scenario of no selection, set all the fitness values to 1.

Mutation Leave the mutation rate at 0.

Migration rate Leave the migration rate at 0.

Initial frequency of the

A allele

Ask students how to determine a reasonable number for this value. Suggest to

them that the frequency of the allele in areas that have little to no malaria is a

reasonable place to start. In this case, the initial frequency is less than 1%, but you

may start with 0.03.

Generations Tell students that some recent studies suggest that the A− allele is only 1000

years old (=40 generations, assuming a 25-year generation length, or 50 genera-

tions assuming a 20-year generation length).

Number of populations Begin with 1, but increase the number as students become comfortable interpret-

ing the results of the simulation.

In a run of 1000 populations with the simulation for these settings, none achieved an allele frequency as high as 0.25 when using population sizes of 10,000, 1000, and 500. With a population size of 100, 15 populations out of 1000 got higher allele frequencies than 0.25.

16. Ask students to work in groups of three to devise a question they would like to test using the model. Next, ask students to write a step-by-step procedure outlining the data they will collect to answer the question and possibly write a hypothesis. After they collect their data, students should develop a claim based on their evidence that answers the question.

Some students will require help getting started with a useful question. Consider offering them the following examples.

• “Astheclasslearnedinthepracticeproblems,scientistshavecollectedevidence that the recessive A− allele for the G6PD gene affects fitness. An estimate for the frequency of A− in some populations is 0.25. Recent analy-ses suggest that individuals with the homozygous recessive phenotype have


39

a selection advantage of 25 percent. Can natural selection account for the change in allele frequency over 1000 years (the estimate for the age of the A− allele)? Assume the recessive allele was originally at a frequency of 0.05.”

n If students choose this question, make sure to have a discussion about the important role of time in evolutionary studies. In most cases, Darwinian evolution is slow, extending over thousands of generations. When selection is strong, however, adaptation can be relatively fast. Reported values for the strength of selection in this case are perhaps the strongest reported in humans. To test this hypothesis, set the fitness of aa to 1.25 (leave the oth-ers at 1) and put the initial frequency of allele A at 0.95.

• “ResearcherssuggestthattheMed allele for the G6PD gene is from 1600 to 6640 years old. Studies suggest that individuals with the homozygous reces-sive phenotype have a selection advantage of 3.4 percent. Assume the allele acts in a recessive fashion. Could this level of selection account for a change in the allele frequency from 0.02 to 0.2 in some populations?”

n A fitness advantage of 3.4 percent may seem small to students, but in evolu-tionary terms it is quite strong.

• “TheJewishpopulationthathistoricallylivedinKurdistanmayhavelivedas a relatively small population for about 2800 years. Researchers discovered that the Med allele for the G6PD gene is at a very high frequency (0.75). If you assume the allele frequency was 0.05 in the founding population, could this high frequency have arisen by chance?”

n Students may want to start with a population size of 1000 and try from 112 to 140 generations.

n Students may also want to explore the impact of starting with a higher frequency of the Med allele, which could have been the case if the original Jewish settlers of Kurdistan came from a region with a high rate of malaria.

• “InsomeareasinSoutheastAsia,theK76Talleleforthepfcrt gene in P. falciparum is at 100 percent. This allele helps the parasite resist the drug CQ. The P. falciparum from other areas that have low or no malaria have <1 percent of this allele in the population. How strong does selection have to be to have an allele go from <1 percent to 100 percent in 30 years?”

n To keep the simulation simple, assume one generation per year, with the maximum population size.

• “Whateffectdoespopulationsizehaveontheprobabilityofthefixationofaparticular allele by genetic drift?”

n The probability of the fixation of an allele goes up as population size goes down.


40

• “Humangroupsrarelyarecompletelyisolated,sothereismigrationfromone population to another. What effect does migration have on the amount of time it takes for a population to change by natural selection?”

n Migration between populations makes populations more similar. The higher the migration rate, the longer it takes for populations to change relative to each other, given the same amount of selection.

• “Canasmallselectiveadvantageleadtolargechangesinallelefrequencyovera long period of time?”

n Students should be able to determine that even small selective advantages, advantages that would be difficult to detect experimentally, do lead to large changes in allele frequencies over time.


Note: Depending on how you structured the previous day, you may need to begin Day 6 by reviewing student homework problems from Master 3.3.

17. Decide on a mechanism to have students share the results of their findings, based on the time you have available, and implement the approach.

One option is to have students write out their claims and evidence on chart paper that can be displayed in the classroom. Students would be responsible for visiting at least two other posters and giving feedback on the design and conclusions for the investigation.

Another option is to have students hand in their work, and then you select two or so examples on the following day as exemplars.

18. End the lesson by asking students to reflect in their notebooks on how mathemati-cal models add to the evidence for evolution. Also ask them how the results from the model allow scientists to make predictions about the future of populations.

Malarialesson 4: Beyond G6PD

41

l e s s O n 4

Beyond G6PD

lesson summary

Brief DescriptionThe goal of the lesson is for students to apply what they have learned about how malaria has influ-enced the frequency of alleles associated with G6PD to other human genes whose allele frequencies have also changed in response to malaria. Students will again work in teams to develop a scientific summary report or otherwise creative presentation describing how malaria has shaped the fre-quency of alleles for at least one more gene. This final product serves as a summative assessment.


• understandthetremendousimpactofmalariaonhumanhealth,• usedataandevidencetodevelopanargumentthatnaturalselectionhasshaped

human diversity, • usetheirunderstandingoftheHardy-Weinbergequilibriummodeltosolve

problems related to the coevolution of the malaria parasite and humans,• beabletouseapopulationgeneticssimulationtoinvestigateandinterpret

evolutionary mechanisms such as genetic drift and natural selection, and• betterappreciatethevalueofunderstandingevolution.

Teacher Preparation

Materials and HandoutsStudent HandoutsMaster 4.1 (1 per student)Master 4.2 (Each group gets 1 of the 5 allele data sets.)Other MaterialsAccess to a computer with Internet access (1 for each student pair; 1 for the teacher [optional])Different-colored pens or pencilsPresentation materials (optional)


42

Preparation InstructionsMuch of the work that students do in this lesson can be completed outside of classroom time. Decide on a schedule for completing the work based on how well your students work inde-pendently. Also decide if you want students to present their work orally, with a poster or a written report, or in some other creative way. Students will again need to have access to the population genetics simulation program from Lesson 3 (PopG Genetic Simulation Program, http://evolution.gs.washington.edu/popgen/popg.html).

If you choose to show the optional Howard Hughes Medical Institute video The Making of the Fittest: Natural Selection in Humans in Step 3, make sure you can access the BioInteractive website, http://www.Biointeractive.org/making-fittest-natural-selection-humans, on your school computer.

Procedure

Estimated time: 15 minutes on Day 7 to make the assignment; 10 minutes in a following period to hold a summary discussion, longer if you do class presentations

Note: This lesson serves as an authentic summative assessment.


1. Explain to students that they have just begun to get a sense of how human diversity and the diversity of the malaria parasite are shaped by the coevolution between the two species. The skills and concepts they are learning sets them up to further under-stand this relationship and, importantly, to explain many kinds of evolutionary change. The goal of this final lesson is to have students demonstrate what they have learned as they develop an explanation for patterns of diversity in alleles for genes influenced by malaria that they have not studied yet.

You may want to make the analogy that the previous lessons involved practice, similar to drills at soccer practice. But the ultimate goal is for students to develop explanations on their own so they can solve problems, similar to inter-squad soccer games. Understand-ing and explaining changes in humans and Plasmodium might very well help us respond to malaria more effectively, which will save lives. Your role as a teacher is to coach and support, but it is the individual student who must ultimately construct explanations on his or her own.

2. Tell students that they will again work in groups to develop a scientific summary report or otherwise creative presentation describing how malaria has shaped the frequency of alleles for at least one more gene. Give each student a copy of Master 4.1 and ask students if they have any questions on how they will be evaluated. Tell students when the assignment will be due and the format for the final product.



http://www.Biointeractive.org/making-fittest-natural-selection-humans


43

Each group will be responsible for the following tasks for its assigned allele.• Describehowthegeneaffectsthephenotypeofanindividual.• Describehowtheproductofthegenemayprotectagainstmalaria.• Describeanypossiblesideeffectsofhavingcertainalleles.• Summarizesimulationstoexplorewhetherornotcertainobservedallelefrequencies

could have arisen in a population by chance or by natural selection.• WriteatleastoneHardy-Weinbergproblemusingthegenethegroupisstudyingas

an example.• Writeafullexplanationforhownaturalselectioncouldexplainhowpopulations

with extreme allele frequencies evolved over time.

You may want to mix up groups so students have the chance to work with other classmates.

3. GiveeachgroupacopyofoneofthefivealleledatasetssummarizedonMaster4.2.

The first allele discussed is the sickle cell allele of the beta-globin gene. Consider assign-ing this allele to students who have not heard this classic story or to a group that finds the material more challenging. You may want to recommend the excellent video from HHMI on sickle cell (go to http://www.Biointeractive.org/making-fittest-natural-selec-tion-humans and select the video The Making of the Fittest: Natural Selection in Humans). The video can be played directly online by clicking on the picture or be downloaded to your computer by right-clicking on any of the links to the right under Download this item and then Save Link As. The most complex gene is HLA-B. Consider assigning this gene to groups that find the material less challenging.

As students conduct the PopG Genetic Simulation Program (http://evolution.gs.wash-ington.edu/popgen/popg.html), tell them to limit themselves to population sizes of 10,000 and 1000. Also, if the initial frequency of an allele is not included in their infor-mation, ask them to use an initial frequency of 0.01 or 0.03.

When investigating the role of natural selection using the simulation, consider the fol-lowing information for the five different alleles.

• DataSet1:Hemoglobin,beta(HBB); S (sickle cell) allele: In an area with high rates of malaria, the heterozygotes should have the highest fitness values. Homozygous recessive genotypes should have the lowest fitness.

• DataSet2:Hemoglobin,beta(HBB); C allele: In an area with high rates of malaria, the heterozygotes and homozygotes for the C allele should have the highest fitness values.

• DataSet3:Hemoglobin,beta(HBB); E allele: In an area with high rates of malaria, the heterozygotes should have the highest fitness values.






44

• DataSet4:Majorhistocompatibilitycomplex,classI,B(HLA-B); allele HLA-B53: In an area with high rates of malaria, the heterozygotes and homozygotes for the HLA-B53 allele should have the highest fitness values.

• DataSet5:Atypicalchemokinereceptor1(ACKR1), Duffy blood group, chemo-kine receptor (DARC); FYB-erythroid silent (ES) or Duffy “null” allele: In an area with high rates of malaria, homozygotes for the ES allele should have the highest fitness values.

You may want to collect and review all the Hardy-Weinberg questions students generate. All the useful questions can be compiled into a review test that students can use as they approach the AP exam.

lesson 4, follow-uP z z z

4. Collect and grade each assignment according to the rubric on Master 4.1. As you can,includespecific,concretefeedbackonthestudents’explanationsofnaturalselection. Give teams time outside of class to address all your feedback. Tell students that all revisions must be in a different color and in the white space that surrounds the original explanation. Tell students that they may earn up to 50 percent more points on their original score based on the quality of revisions.

This approach sends a clear message to students that meaningful revisions are an import-ant learning tool.

5. Hold a summary discussion about what students learned about the impact of malaria on human diversity. Ask students why different groups of people have responded differently to malaria from an evolutionary standpoint.

The final question gives you an opportunity to address the common misconception that natural selection leads to perfection. A useful comparison is the effect of HBB allele S, which protects against malaria in heterozygotes but causes sickle cell disease in homozy-gotes, and allele C, which also provides protection from malaria, but without the associa-tion to a debilitating disease. Allele S differs from allele C only in the specific amino acid that gets replaced. If allele C had arisen instead of allele S, many people would be spared sickle cell anemia. Unfortunately, evolution does not lead to perfection, but only works with the genetic variation that is present and in a particular environmental context.

In the summary discussion, emphasize that by learning to develop explanations based on evidence for natural selection, students have developed skills that enable them to make a broad range of explanations in the natural world and to ask questions that will lead to new, important, and exciting discoveries.

Malariareferences

45

references

Centers for Disease Control and Prevention. (2015). Malaria facts. Retrieved from http://www.cdc.gov/malaria/about/facts.html.

Chinevere, T. D., Murray, C. K., Grant, E., Jr., Johnson, G. A., Duelm, F., & Hospenthal, D. R. (2006). Prevalence of glucose-6-phosphate dehydrogenase deficiency in U.S. Army personnel. Military Medicine, 171(9), 905–907.

G6PD Deficiency Association. (2015). Retrieved from http://www.g6pd.org.World Health Organization. (2014, May). The top 10 causes of death (Fact Sheet No. 310).

Retrieved from http://www.who.int/mediacentre/factsheets/fs310/en/index.html.



http://www.g6pd.org


MalariaMasters

46

Masters

LESSON 1: Changes in a Long-Term RelationshipMaster 1.1, Malaria around the World . . . . . . . . . . . . . . . . . . . . . . . . . . projectionMaster 1.2, Malaria’s Parasite in Humans . . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 1.3, Fighting Malaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 1.4, Explanations for Change. . . . . . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 1.5, Four Explanations for Change in Malaria Parasites . . . . . . . . projectionMaster 1.6, Experiments Exploring Changes in Malaria’s Parasite . . . . . . . projection or student copiesMaster 1.7, Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 1.8, Analysis Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . student copies

LESSON 2: Malaria and Human DiversityMaster 2.1, Investigating a Health Problem . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 2.2, G6PD Deficiency Allele Maps. . . . . . . . . . . . . . . . . . . . . . . . projectionMaster 2.3, G6PD Data Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . student copiesMaster 2.4, Natural Selection Template . . . . . . . . . . . . . . . . . . . . . . . . . . projection

LESSON 3: Malaria and Population GeneticsMaster 3.1, Malaria Story Line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . projectionMaster 3.2, A Mathematical Model for Investigating Evolution . . . . . . . . student copiesMaster 3.3, Using the Hardy-Weinberg Equilibrium Model . . . . . . . . . . . student copiesMaster 3.4, A Simulation Tracking Allele Frequency over Time . . . . . . . . . projection

LESSON 4: Beyond G6PDMaster 4.1, Malaria’s Effect on Humans Rubric . . . . . . . . . . . . . . . . . . . . student copiesMaster 4.2, Beyond G6PD Data Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . student copies

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.1

Malaria around the World

Figure 1. Red indicates that malaria is found everywhere in the region. Yellow areas are those with moderate levels of malaria or areas with both high and low rates of malaria. Green means that there is no malaria. Source: Centers for Disease Control and Prevention, 2012.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.2

Malaria’s Parasite in humans

Malaria is a terrible disease that has long affected humans. The disease-causing agent, also called a vector, is a single-celled parasite in the genus Plasmodium. Though there are four species of malaria parasites that affect humans, half of all the cases of malaria and about 95 percent of the deaths are caused by the species Plasmodium falciparum. All species of Plasmodium that affect humans rely on two different hosts to complete their life cycles—mosquitoes and humans.

Watch the Howard Hughes Medical Institute video Malaria: Human Host, on the life cycle of P. fal-ciparum once it is in humans. As you watch, answer the following questions.

Questions 1. How does the malaria parasite move from the mosquitoes to humans?

2. After entering the circulatory system, in what organ does the malaria parasite reside?

3. What cellular process takes place in the malaria parasite once it is inside the liver?

4. How many offspring can one parasite make in one liver cell?

5. Where does the parasite move after leaving the liver?

6. What does the parasite do inside red blood cells?

7. What are the effects of malaria?

8. What percentage of people are likely to contract malaria each year?

9. Who dies from malaria?

10. Over a period of two weeks, how many new parasite individuals could be formed starting with just one parasitic cell inside a human? Use the following information to solve the problem.

• Initialinfectionofalivercell:Infectionlastssixdays,andupto40,000indi-viduals are formed.

• Redbloodcellinfection:Everytwodays,eachcellcanmakeupto24newindividuals.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.3

Fighting Malaria

People have been looking for a cure for malaria since antiquity. In the early 1900s, there was an intense search for drugs to treat malaria, as the one major drug of quinine was becoming less effective. Researchers examined a broad range of chemicals, including a dye called methylene blue that is found in many high school biology labs. Eventually, researchers discovered the compound called chloroquine, or CQ. Near the end of World War II (1939–1945), CQ came into widespread use. The drug’s success was spectacular, as it was relatively cheap to develop and had few side effects. In fact, CQ is one of the most effective drugs ever developed to fight an infectious disease. At one point, in Africa alone, 1190 tons (1080 metric tons, or hundreds of millions of treatment courses) of CQ was used each year.

Because of CQ’s effectiveness, along with the effects of the chemical agent DDT, which helped control mosquitoes, some health officials in the 1950s thought that malaria would be eliminated. Within a decade of the widespread use of CQ, however, problems developed, first in Southeast Asia. The problem was that some people were taking CQ, but it was no longer effective in killing the parasite. In other words, the para-site became resistant to the drug. Figure 1 shows the spread of resistant forms of the malaria parasite across the world. With the rise in resistance, the illnesses and deaths associated with malaria resurged, especially among children in Africa. For example, in Senegal, there was up to an 11-fold increase in deaths due to malaria in children aged zero to four because of CQ resistance (Talisuna, Bloland, & D’Alessandro, 2004).

Figure 1. The spread of resistance to chloroquine (CQ) in Plasmodium falciparum over time by country. Darker shades indicate a higher percentage of resistance. Source: Cole, 2012.

Question 1. How would biologists explain how the ability to survive in the presence of CQ developed

in some populations of Plasmodium falciparum? Include all the elements you think are needed for a full explanation. Put your answer on a new blank page and leave a lot of space around the answer.

ReferenceTalisuna, A. O., Bloland, P., & D’Alessandro, U. (2004). History, dynamics, and public health importance of malaria

parasite resistance. Clinical Microbiology Reviews, 17(1), 235–254. doi:10.1128/CMR.17.1.235-254.2004.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.4 (page 1)

explanations for change

Accurately describing the fact that lineages of organisms change over time and explaining how they change has been a challenge throughout most of human history. Below are four general ways that humans have tried to explain change over time. Your task is to begin to recognize these different types of explanations and to ultimately use data and evidence to choose the explanation that best fits the evidence.

Why consider a range of explanations? Considering a range of explanations is what scientists do. A major component in getting better at generating scientific explanations is to know and understand alternative explanations, even if they are incorrect. This understanding empowers you with the intellectual flexibility to recognize valid and invalid explanations, which ultimately leads to a greater chance of success.

Explanation 1Species (and the populations that compose them) do not fundamentally change over time.

In this view, species have some fundamental power or essence that makes the species what they are. This essence does not change. In other words, individuals may vary in some ways within species, but these are superficial compared to their fundamental essence. “Important” traits in species should not change. Species cannot change from one “kind” to another “kind.”

Explanation 2Species (and the populations that compose them) change when the environment changes. Use and disuse of certain parts of an organism cause them to develop or deteriorate. These acquired charac-teristics can be passed from parents to offspring, which causes adaptation of the organisms to their environment.

This view was proposed by Jean-Baptiste Lamarck (1744–1829), who was, in many ways, the founder of modern biology. In this view, the use of certain organs or other structures would cause an increase in these organs or structures in individuals over time, which could be passed to off-spring. For example, if a giraffe stretched its neck to reach higher leaves, it could lengthen its neck. The offspring would then have longer necks, too. Similarly, when an organ or other structure was not used, it would wither and eventually disappear from a population because it was not used.

Explanation 3Species (and the populations that compose them) change when the environment changes. Vari-ations among individuals are caused directly by the environment or because an individual needs them to change or realizes they should change. In other words, every difference has a purpose, based on need.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.4 (page 2)

This view is similar to Explanation 2, but it suggests that organisms change because they want or need to change. An example would be that giraffes have longer necks because they needed to reach higher leaves. Also, whales lost their legs because they did not need them anymore in an aquatic environment.

Explanation 4Species (and the populations that compose them) change due to the process of natural selection. Natural selection is described by the four processes below.

• Variation:Individualsdifferforsometraitofinterest.• Inheritance:Thevariationforthetraitofinterestisatleastpartiallyinherited

(passed from parents to offspring). The origin of the variation stems from mutations (broadly speaking) and the recombination that accompanies sexual reproduction. The genetic variation may have arisen many generations in the past.

• Selection:Becauseofbioticpotential,moreoffspringwillbebornthancansur-vive. The outcome of this fact is competition among individuals. As a result, some individuals with a trait survive and leave relatively more offspring compared to individuals that do not have the trait. In other words, individuals with the trait have increased fitness. Selection depends on the specific context of a species. Traits that are beneficial in one environment may cause problems in another environment.

• Adaptation:Thefrequencyofthetraitthatimprovesfitnesswillincreaseinthepop-ulation over time, as will the alleles that affect the trait. This process can take many generations and extend over very long periods of time.

Tasks 1. Work with your team to create four bumper stickers, one for each type of explanation.

Bumper stickers are concise, often witty summary positions that help us think and draw a distinction between one way of thinking and another. For example, a bumper sticker for mitosis might be “Divide and Multiply!,” one for meiosis might be “Our sex cells do more with half the chromosomes than other cells do all day,” or one for ATP might be “The small change we need.” Then write a short explanation of each bumper sticker.

2. Work as a team to practice explaining the development of resistance to chloroquine (CQ) in Plasmodium falciparum using each type of explanation.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.5

Four explanations for change

in Malaria Parasites

Explanation 1: No Fundamental ChangeThe populations of Plasmodium falciparum that are resistant might differ from other populations, but nothing fundamental about the parasites has changed. As a result, none of the information in the hereditary material making up the parasites will have changed.

Explanation 2: Adaptation Due to Acquired CharacteristicsIndividual parasites initially had a poor ability to live in the presence of chloroquine (CQ). When the environment of the parasite changed and CQ was present, individuals started using charac-teristics to help them survive better. These individuals changed and passed this ability on to their offspring. Over time, individuals became better at living in the presence of CQ.

Explanation 3: Change Based on Want or NeedIndividual parasites initially had a poor ability to live in the presence of CQ. When the environ-ment of the parasite changed and CQ was present, individuals recognized that they needed to change. Because of this need, individuals developed traits to help them survive. These individuals changed and passed this ability on to their offspring. Over time, individuals changed because they wanted or needed to change.

Explanation 4: Natural Selection• Variation:IndividualswithinP. falciparum populations varied in their ability to live

in the presence of CQ.• Inheritance:TheabilitytosurviveinthepresenceofCQisatleastpartiallyinher-

ited. Changes to DNA either recently or in the past cause the variation and explain how it is inherited.

• Selection:IndividualparasitesthatcouldliveinthepresenceofCQsurvivedandleft more offspring than other parasites did.

• Adaptation:ThefrequencyoftheabilitytoliveinthepresenceofCQincreasedinthe population over time, as did the alleles that affect the ability to live in the pres-ence of CQ.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.6 (page 1)

experiments exploring changes

in Malaria’s Parasite

Experiment 1Researchers collected different strains of Plasmodium falciparum from across the world. Some sam-ples were from different parasitic individuals in the same region. They then exposed the parasites to chloroquine, or CQ, and determined the ability of each strain to grow and survive at different CQ doses. Researchers reported the concentration at which the drug inhibits parasite growth by 50 percent (IC

50). CQ-resistant strains have IC

50 values greater than a CQ concentration of 100

nanomolars (nM).

Task 1. Make a prediction of what you would expect to find using each of the four explanations.

Another way of approaching this task is to ask, “Should variation exist among individual parasites?”

Experiment 2Researchers determined the DNA sequences for a large portion of the genome in 227 P. falciparum individuals from Asia, Africa, and Oceania.


Another way of approaching this task is to ask, “Should variation in DNA exist among individual parasites?”

Experiment 3Researchers have gathered evidence that a particular gene in P. falciparum may be related to CQ resistance. The gene called pfcrt (or sometimes just crt) codes for the Plasmodium falciparum chlo-roquine resistance transporter protein (PfCRT), which has 424 amino acids. This protein is found in the membrane of the intracellular digestive vacuole of the parasite (see Figure 1). The digestive vacuole is similar to a lysosome. Some forms of the PfCRT protein transport CQ out of the diges-tive vacuole. If CQ is transported out of the membrane, the parasites become resistant to the drug.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.6 (page 2)

Figure 1. Cartoon showing the structure of the PfCRT protein embedded in the digestive vacuolar membrane of Plasmodium falciparum. Numbers indicate the number of specific amino acids in the protein. Source: Ecker, Lehane, Clain, & Fidock, 2012.

Scientists determined the sequence of the amino acids that make up PfCRT in different strains of P. falciparum from across the world. Some of the strains were resistant to CQ, and some were not.

Task 3. Predict what patterns (including no pattern) you would expect to find using each of the

four explanations.

Another way of approaching this task is to ask, “Should variations in Pf CRT proteins be associated with CQ resistance?”

Experiment 4Researchers developed a method to move the allele for the pfcrt gene from one P. falciparum indi-vidual to another. They were able to move the pfcrt allele from a resistant strain into a P. falciparum strain that was previously sensitive (not resistant). A control strain had a different allele moved. The focus question for this experiment was, “Does moving only the pfcrt allele between strains bring about resistance?”

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.6 (page 3)


Another way of approaching this task is to ask, “Should changing one allele in the parasite affect its resis-tance to CQ?”

Experiment 5Researchers discovered in their analysis of PfCRT proteins that all the resistant parasites had a change in the 76th amino acid from lysine (a charged amino acid, called K76) to threonine (an uncharged amino acid, labeled 76T). Using the genetic code, researchers know the DNA sequence of the alleles that cause the different forms of the protein. Scientists surveyed the frequency of the two alleles in different geographic regions, some that have high rates of malaria and high rates of CQ use and some that have low rates of malaria and no use of CQ.

Task 5. Use each type of explanation to predict the frequency of the allele that causes CQ resis-

tance in geographic areas that do or do not have high rates of malaria.

Experiment 6After health professionals recognized that CQ was no longer effective for many patients, some countries like Malawi decided to stop using CQ. Malawi has high rates of endemic malaria. Sci-entists were able to access samples of P. falciparum from the last year the drug was used (1992) in Malawi. They also had samples up until 2005, 13 years after the use of the drug stopped.

Task 6. Predict what you expect to happen to the frequency of the allele that causes CQ resis-

tance over time.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.7 (page 1)

experimental results

Experiment 1Results: Selected sample results are shown in Figure 1.

Figure 1. The degree to which samples of Plasmodium falciparum from different parts of the world are inhibited by the drug chloroquine (CQ). An IC

50 value of 100 nanomolars (nM) or higher is considered to be resistant to CQ.

Task 1. Use the evidence to make a claim that answers the question, “Does variation exist among

Plasmodium falciparum individuals for resistance to CQ?” Make sure to refer to the evidence.

Experiment 2Results: Researchers had high confidence that they identified 86,158 places in the genome where one nucleotide differed in at least 1 of the 227 individuals. P. falciparum’s genome has 23.3 mil-lion bases on 14 chromosomes, so there is approximately 1 change in a nucleotide every 270 bases (23,300,000/86,158). This is a remarkably high rate of change in the DNA sequence, orders of magnitude higher than the average rate of change (Eckland & Fidock, 2007).

Task 2. Use the evidence to make a claim that answers the question, “Does variation in DNA

exist among individual parasites?” Make sure to refer to the evidence.

Experiment 3Results: The amino acids at 10 different positions in the PfCRT protein are shown in Table 1.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.7 (page 2)

Task 3. Use the data in Table 1 to make a claim that answers the focus question, “Are specific

variations in PfCRT proteins associated with CQ resistance?”

Table 1. Amino acids in the PfCRT protein that differ among the P. falciparum individuals sampled.

Region Line 72 74 75 76* 97 220 271 326 356 371

Chloroquine-

sensitive lines

Thailand T2/C6 C M N K H A Q N I R

All regions Malaysia Camp/A1 C M N K H A Q N I R

Sudan 105/7a C M N K H A Q N I R

South Africa FAB9 C M N K H A Q N I R

Kenya K39a C M N K H A Q N I R

The

Netherlands

NF54a C M N K H A Q N I R

Haiti Haiti C M N K H A Q N I R

Honduras HB3a C M N K H A Q N I R

Chloroquine-

resistant lines

Indochina Dd2a C I E T H S E S T I

Southeast Asia

and Africa

Vietnam V1/S C I E T H S E S T I

Thailand TM284 C I E T H S E S T I

Southeast Asia FCB C I E T H S E S I I

Cambodia Jcl C I E T H S E S T I

Sudan 102/1a C I E T H S E S T I

South Africa RB20 C I E T H S E S I I

Kenya KMWII C I E T H S E S I I

Mali S35CQa C I E T H S E S I I

South America Brazil 7G8a S M N T H S Q D L R

Brazil DIV30a S M N T H S Q D L R

Ecuador Ecu1110 C M N T H S Q D L R

Colombia Java C M E T Q S Q N I T

Colombia IAJa C M E T Q S Q N I T

Source: Fidock, D. A., Nomura, T., Talley, A. K., Cooper, R. A., Dzekunov, S. M., Ferdig, M. T., Ursos, L. M. B., Sidhu, A. B. S., Naudé, B., Deitsch, K. W., Su, X.-z., Wootton, J. C., Roepe, P. D., & Wellems, T. E. (2000). Mutations in the P. falciparum digestive vacuole transmembrane protein PfCRT and evidence for their role in chloroquine resistance. Molecular Cell, 6(4), 861–871. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944663/table/T1/.Note: The numbers in the column headings refer to specific amino acids. The 20 amino acids in humans are each assigned a specific one-letter abbreviation. *You will learn more about amino acid 76 later in the data analysis.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944663/table/T1/

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.7 (page 3)

Experiment 4Results: Selected sample results are shown in Figure 2.

Figure 2. Results for Experiment 4 showing the degree to which samples of P. falciparum from the experiments are inhibited by the drug CQ. An IC

50 value of 100 nM or higher is considered to be resistant to CQ. Source: Data from

Sidhu, Verdier-Pinard, & Fidock, 2002.

Task 4. Make a claim that answers the focus question, “Does changing one allele in the parasite

affect its resistance to CQ?” Use the appropriate evidence in your claim.

Experiment 5Results: The frequency of the allele that causes the replacement of a lysine amino acid at position 76 with a threonine (called K76T) for different regions is shown in Table 2.

Table 2. Population frequency of the K76T allele in different geographic regions.

Region Frequency of K76T

Africa 0.57

Southeast Asia 1.0

Papua New Guinea 0.94

Areas with very little to no malaria <0.01

Source: Manske, M., Miotto, O., Campino, S., Auburn, S., Almagro-Garcia, J., Maslen, G., . . . Rayner, J. C. (2012). Analysis of Plasmodium falciparum diversity in natural infections by deep sequencing. Nature, 487(7407), 375–379.

Task 5. Use the data to make a claim about the frequency of the allele that causes CQ resistance

in different regions.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.7 (page 4)

Experiment 6Results: The frequency of the allele that causes a threonine to be at amino acid position 76 instead of a lysine (called K76T) over time in Malawi is shown in Table 3.

Table 3. Population frequency of the K76T allele in Malawi, 1992–2005.

Year Frequency of K76T

1992 0.85

1994 0.48

1996 0.24

1999 0.18

2000 0.13

2001 0.00

2005 0.00

Source: Kublin et al., 2003; Laufer et al., 2010.

Neighboring countries did not stop using CQ. In 1999, the frequency of the K76T allele in Zam-bia was 0.92. In 2001, the frequency of the K76T allele in southern Mozambique was 0.91.

Task 6. Use the data to make a claim about the frequency of the allele that causes CQ resistance

when the environment for the parasite changes.

ReferencesEkland, E. H., & Fidock, D. A. (2007). Advances in understanding the genetic basis of antimalarial drug resistance.

Current Opinion in Microbiology, 10(4), 363–370.Kublin, J. G., Cortese, J. F., Njunju, E. M., Mukadam, R. A. G., Wirima, J. J., Kazembe, P. N., . . . Plowe, C. V. (2003).

Reemergence of chloroquine-sensitive Plasmodium falciparum malaria after cessation of chloroquine use in Malawi. Journal of Infectious Diseases, 187(12), 1870–1875.

Laufer, M. K., Takala-Harrison, S., Dzinjalamala, F. K., Stine, O. C., Taylor, T. E., & Plowe, C. V. (2010). Return of chloroquine-susceptible falciparum malaria in Malawi was a reexpansion of diverse susceptible parasites. Journal of Infectious Diseases, 202(5), 801–808.

Manske, M., Miotto, O., Campino, S., Auburn, S., Almagro-Garcia, J., Maslen, G., . . . Rayner, J. C. (2012). Analysis of Plasmodium falciparum diversity in natural infections by deep sequencing. Nature, 487(7407), 375–379.

Sidhu, A. B. S., Verdier-Pinard, D., & Fidock, D. A. (2002). Chloroquine resistance in Plasmodium falciparum malaria parasites conferred by pfcrt mutations. Science, 298(5591), 210–213.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 1.8

analysis Questions

1. Compare and contrast the evolution of resistance to chloroquine (CQ) in Plasmodium falciparum to resistance to antibiotics in bacteria.

2. The HIV virus very quickly evolved resistance to some of the first medicines developed to treat AIDS. Using an understanding of evolution, health professionals developed a new treatment protocol for people with HIV called highly active antiretroviral therapy (HAART). This therapy involves administering three or more drugs to a patient at once to help avoid the evolution of resistance. With this in mind, suggest an approach for treating people with malaria that may help counter the evolution of resistance to CQ.

3. The parasite P. falciparum shows a great deal of diversity. Use this information to make a prediction about the ease or difficulty in developing a vaccine for malaria.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.1 (page 1)

investigating a health Problem

reading z z z

The time was 1925. Malaria was having a large impact on public health, as it has throughout human history. The main treatment for malaria at the time was quinine, but 95 percent of the supply of the drug came from Java and Sumatra, which were controlled by the Dutch. Due to many conflicts in tropical regions, quinine became a military resource. Germany was cut off from the Dutch supply, and it sought an alternative. One drug that looked promising was called primaquine.

At the same time, the United Fruit Company was actively becoming a major exporter of bananas from malaria-prone regions in Central and South America. It sponsored a study of primaquine in Cuba. In this study, Dr. Wilhelm Cordes gave the drug to 36 patients. Unfortunately, some patients developed anemia, cyanosis, and cramps when given the drug, and two patients died. The resulting health problem is called acute hemolytic anemia. Acute hemolytic anemia is a con-dition in which red blood cells are rapidly destroyed. The patients who had adverse effects were primarily West Indian migrants of African descent, who dominated the plantation labor force.

Analysis 1. Three primary causes of disease are infection by pathogens, genetic effects, or exposure

to toxins or other extrinsic factors found in the environment. Use evidence from the reading to predict the cause of the condition that made some people react poorly to the drug.

2. Describe the data you would like to collect to further test the prediction you made in the previous question.

reading z z z

Investigating the Health Problem

Researchers wondered whether the toxicity of the drug primaquine was due to the drug being gen-erally toxic to some people or if there was something different in some people’s red blood cells that caused them to react to the drug.

To answer this question, researchers used a method to label the red blood cells from different indi-viduals, using radioactive chromium (51Cr). During the 1940s, prisoners in Stateville Penitentiary

z z z

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.1 (page 2)

in Illinois participated in a research project. Two groups of prisoners participated: (1) those who were susceptible to hemolytic anemia if they took primaquine (primaquine sensitive), and (2) those who did not suffer ill effects from taking the drug (primaquine tolerant).

In the first experiment, some blood from a primaquine-sensitive prisoner was removed, labeled with 51Cr, and then transfused into four people who were tolerant. Three of the people then received primaquine, and the number of labeled red blood cells was monitored. The results are shown in Figure 1.

Figure 1. The fraction of red blood cells from a primaquine-sensitive subject (labeled with 51Cr) remaining after the blood was transfused into primaquine-tolerant people who then took primaquine. The control person did not take primaquine. Primaquine was given to Prisoners 2, 3, and 4 on Day 10 (arrow). Source: Adapted from Beutler, 2008.

In the second experiment, some blood from a primaquine-tolerant prisoner was removed, labeled with 51Cr, and then transfused into two people who were primaquine sensitive and one who was tolerant. One of the sensitive individuals and the tolerant individual were given primaquine, and the other sensitive person was not given the drug. The number of labeled red blood cells was moni-tored over time. The results are shown in Figure 2.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.1 (page 3)

Figure 2. The fraction of red blood cells from a primaquine-tolerant subject (labeled with 51Cr) remaining after the blood was transfused into two individuals who were primaquine sensitive and one who was tolerant. One of the sen-sitive individuals and the tolerant individual were given primaquine, and the other sensitive person was not given the drug. Source: Adapted from Beutler, 2008.

Analysis 3. Use the data in Figures 1 and 2 to make a claim about whether the toxicity of the drug

primaquine was due to the drug being generally toxic to some people or if there was some-thing different in some people’s red blood cells that caused them to react to the drug.

4. The data in Figures 1 and 2 came from research done on prisoners in the United States during World War II. The prisoners gave their full consent and volunteered for their role. By participating, they could receive reduced sentences. This type of research is forbidden today. What ethical issues arise for you in this situation?

z z z

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.1 (page 4)

reading z z z

TheRoleoftheEnzymeG6PD

Researchers eventually discovered that people whose red blood cells were destroyed with pri-maquine had a defect in a specific enzyme called glucose-6-phosphate dehydrogenase (G6PD). This condition is called G6PD deficiency. G6PD is active in almost all types of cells in the human body, as it plays an important role in carbohydrate metabolism. The role of G6PD is especially crucial in red blood cells, where it helps protect the cells from damage caused by oxygen radicals.

More specifically, G6PD catalyzes the first step in a chemical pathway that eventually converts glu-cose into the monosaccharide found in nucleotides (ribose-5-phosphate). As shown in Figure 3, the chemical reaction catalyzed by G6PD produces a molecule called NADPH. NADPH is an import-ant electron shuttle and plays a role in protecting cells from oxygen radicals. NADPH is especially useful in red blood cells, which carry a large amount of oxygen but lack other enzymes that make NADPH. Individuals who are deficient in G6PD respond poorly to primaquine because this drug causes oxygen radicals to form.

Figure 3. The enzyme G6PD catalyzes an important reaction in carbohydrate metabolism. The NADPH that is formed helps protect cells from reactive oxygen. GSSG means “oxidized glutathione”; GSH means “reduced glutathi-one.” Source: Adapted from Frank, 2005.

Analysis 5. Another important molecule that protects cells from oxidative stress is called glutathione.

When glutathione gains an electron (it gets reduced, called GSH), it, too, protects cells from oxidative damage.

a. Use Figure 3 to determine the source of electrons to reduce glutathione.b. If the enzyme G6PD is impaired, predict what will happen to the amount of the

reduced form of glutathione.

z z z

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.2

g6Pd deficiency allele Maps

Figure 1. Global map showing the frequency of G6PD deficiency alleles. Source: Howes, Piel, Patil, Nyangiri, Geth-ing, Dewi, . . . Hay, 2012.

Figure 2. Global map showing the frequency of G6PD deficiency alleles as it relates to the presence of malaria. Source: Howes, Piel, Patil, Nyangiri, Gething, Dewi, . . . Hay, 2012.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.3 (page 1)

g6Pd data sets

Data Set 1

Figure 1. Three pedigrees were assembled for three families that have G6PD deficiency.

Analysis 1. Use the data in the three pedigrees to make a claim about the mode of inheritance for

G6PD deficiency.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.3 (page 2)

Data Set 2The G6PD gene is located on the long (q) arm of the X chromosome. More precisely, the G6PD gene is located from nucleotide 154,531,389 to nucleotide 154,547,585 on the X chromosome.

Figure 2. top. A diagram showing the X chromosome from Homo sapiens. Note that the G6PD gene is very close to the gene for blue-green color vision. Also nearby is the gene in which specific mutations cause fragile X syndrome. bottom. The dark boxes represent exons, and the light gray boxes represent introns. Sources: Images adapted from (top) Genetics Home Reference, 2013, G6PD; (bottom) Cappellini & Fiorelli, 2008.

G6PD is approximately 18,500 nucleotides, with 13 exons and 12 introns. The coding region involves 1545 nucleotides, leading to 515 amino acids.

Analysis 2. Do these additional data confirm or contradict the claim you made with Data Set 1?

Explain your answer.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.3 (page 3)

Data Set 3Numerous mutations to the coding region of G6PD have been discovered in humans. Over 140 mutations to the gene affect the amount or activity of the G6PD enzyme. It is one of the most variable genes in the human genome. Five classes of enzyme activity are recognized.

(1) Severe deficiency (<10 percent activity), with chronic hemolytic anemia (2) Severe deficiency (<10 percent activity), with intermittent hemolysis (3) Mild deficiency (10–60 percent activity), with hemolysis occurring with certain stressors (4) Nondeficient variant, with no clinical issues (5) Increased enzyme activity, with no clinical issues

Classes 1, 2, and 3 are called G6PD deficiencies.

Table 1 summarizes information on some of the most common alleles of G6PD.

Table 1. Names and details for five common alleles of G6PD that cause enzyme deficiencies.

AlleleNucleotide coding

position and change

Amino acid number

and change

Area of

high global

concentration

Population

frequencies

(%)

Enzyme

activity (%)

A 376 (from A to G) 126 (from Asn to Asp) Africa 15–40 85

A− 202 (from G to A)

376 (from A to G)

68 (from Val to Met)

126 (from Asn to Asp)

Africa 0–25 12

Med 563 (from C to G) 188 (from Ser to Phe) Middle East /

Mediterranean

2–20 3

Seattle 844 (from G to C) 282 (from Asp to His) Mediterranean — —

Mahidol 487 (from G to A) 163 (from Gly to Ser) Southeast Asia Up to 24 5–32

Source: Tishkoff, S. A., & Verrelli, B. C. (2004). G6PD deficiency and malarial resistance in humans: Insights from evolutionary genetic analyses. Infectious Disease and Host-Pathogen Evolution, 39–74; Hedrick, P. W. (2011). Population genetics of malaria resistance in humans. Heredity, 107(4), 283–304. Note: — means “not reported.”

Analysis 3. Do you think these alleles came about because people wanted or needed them to come

about? Why or why not?

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.3 (page 4)

Data Set 4The results below are from studies that examined the impact of G6PD deficiency alleles on both the malaria parasite and people who have the deficiency.

(1) Researchers collected data that suggest that red blood cells with normal G6PD activity had 2 to 80 times more parasitic growth than G6PD-deficient red blood cells from the same person. In other words, researchers were able to control for all other genetic factors.

(2) Researchers compared the growth of parasites in red blood cells from people with the G6PD A− deficiency allele and the G6PD Med deficiency allele to red blood cells with no G6PD deficiency. Parasite growth is slowest in G6PD-deficient cells.

(3) The most prevalent G6PD deficiency allele in Africa is called A−. This allele is asso-ciated with a major reduction in the risk of severe malaria caused by Plasmodium fal-ciparum. Female heterozygotes for the allele had a 46 percent reduced risk, and male hemizygotes had a 58 percent reduced risk. Males are called hemizygotes because they only have one copy of the X chromosome.

Analysis 4. “Fitness,” in evolutionary terms, means the relative ability of an individual to survive and

reproduce. What do the data suggest about the impact of G6PD deficiency alleles on fitness in areas that have high rates of malaria?

ReferencesHedrick, P. W. (2011). Population genetics of malaria resistance in humans. Heredity, 107(4), 283–304.Tishkoff, S. A., & Verrelli, B. C. (2004). G6PD deficiency and malarial resistance in humans: Insights from evolutionary

genetic analyses. Infectious Disease and Host-Pathogen Evolution, 39–74.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 2.4

natural selection template

Table 1.

Aspect of natural


Variation

Inheritance

Selection

Adaptation

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.1

Malaria story line

Lesson 1: Examined evidence to compare four different explanations for why many malaria parasites

are resistant to antimalarial drugs.

Lesson 2: Investigated how scientific arguments, based on evidence and claims, show support for each

of the major principles of natural selection in some groups of humans in response to malaria.

Lesson 3: Design and conduct an investigation using a simulation based on scientific models to explore

different mechanisms of evolution.

Lesson 4: Develop an explanation for how alleles from other genes have changed in some groups of

humans over time due to natural selection driven by malaria.

Do the same principles of evolution by natural selection apply to humans?

How do biologists use mathematical models and simulations

to further investigate evolution?

How can we apply what we learned to examine other ways in which

people have coevolved with the malaria parasite?

4

4

4

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.2

a Mathematical Model for

investigating evolution

In 1908, Godfrey Hardy (a mathematician) and Wilhelm Weinberg (a physician) independently developed a mathematical model for analyzing genes in populations. Their work outlines the con-ditions that need to be met in order for a population to maintain the same genetic structure over time. The Hardy-Weinberg equilibrium model (H-W model) that they proposed led to one very important insight: if certain assumptions are met, the frequencies of alleles at a specific gene or region of the genome (locus) remain constant from generation to generation. As a result, the H-W model can act as a null hypothesis as biologists explore whether populations are evolving.

How Do Biologists Use the Hardy-Weinberg Equilibrium Model?The H-W model allows biologists to estimate the frequencies of genotypes (for example, AA, Aa, or aa for a gene with two alleles, one of which is dominant) from the frequency of specific alleles (for exam-ple, the frequency of A and a). In other words, it allows biologists to make predictions of what the genotype frequencies should be if a population is not changing. When estimates of genotype frequen-cies in real populations are different from the predictions, biologists can evaluate what specific mecha-nisms are acting to cause change in populations. In other words, they can get insight into evolution.

What Are the Assumptions of the H-W Model?Like all scientific models, the H-W model makes assumptions.

(1) Aninfinitepopulationsize: Small populations are subject to changes due to the chance effects of the small sample (also known as genetic drift).

(2) The absence of migration: There is no movement of individuals or their gametes in or out of a population.

(3) No net mutations: No new alleles are formed by mutation, and existing alleles do not change.

(4) Randommating: Individuals do not choose their mates. (5) The absence of selection: All individuals have an equal probability of survival, and they

reproduce at the same rate.

As you would suspect, these conditions are rarely, if ever, met in nature. Still, the H-W model pro-vides a powerful framework that other biologists have extended to further explore and make predic-tions about evolution.

You may also note that the five assumptions correspond to the five mechanisms that can cause evo-lution in populations: genetic drift, migration, mutations, nonrandom mating, and selection.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.3 (page 1)

using the hardy-Weinberg

equilibrium Model

The simplest situation in which to use the Hardy-Weinberg (H-W) model is for one gene (or locus) with only two alleles.

A1 = one of the two alleles (for example, a DNA sequence of AATAAGTGG),

A2 = the second allele (for example, the DNA sequence AATCAGTGG)

Imagine that we collected all the alleles in a population of diploid organisms. We could calculate the frequency of A

1 using the following formula.

number of copies of A1 in the population

total number of all the alleles in the population

We could use the same approach to calculate the frequency of A2.

number of copies of A2 in the population

total number of all the alleles in the population

Biologists often use another symbol to represent the frequencies of these alleles.

p = the frequency of A1,

q = the frequency of A2

You may also recognize that if there are only two alleles, there are only three possible genotypes: A

1A

1, A

1A

2, or

A

2A

2.

Situation 1Now we will walk through a step-by-step procedure to practice using the H-W model to calculate expected genotype frequencies if you are given allele frequencies.

Sample Problem In Lesson 1, you learned about a specific allele called K76T in Plasmodium falciparum for the pfcrt gene that enables individuals to be resistant to the drug CQ (chloroquine). In one study, the fre-quency of the K76T allele in Africa was 0.57. Assume just one other allele is in the population. Its frequency would be 1 − 0.57 = 0.43. Use the H-W model to calculate the expected genotype frequencies in the next generation for the diploid phase of the P. falciparum life cycle.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.3 (page 2)

Step What you need to do

1 Define what is known. In this case, let’s call the K76T allele A1. So, in this case, p = 0.57. The other allele is

A2 and q = 0.43.

2 Decide what you need to figure out. In this case, you need to calculate the expected frequency of three possible

genotypes for the diploid individuals: A1A1, A1A2, or A2A2.

3 Use mathematical reasoning to solve for the probability of getting the A1A1 genotype. If all the assumptions

of the H-W model hold, the probability of getting A1A1 is equal to the probability of first selecting A1 from all the

alleles multiplied by the probability of selecting another A1 from all the alleles. The probability of selecting A1 = the

frequency of A1 = p. So, the probability of selecting A1 twice = p × p = p2.

In this problem, p2 = (0.57)2 = 0.33.

4 On your own, use the same reasoning to figure out how to calculate the probability of getting the A2A2

genotype. You should get q2 = 0.18.

5 Use further reasoning to calculate the probability of getting the genotype A1A2. There are two ways to get the

genotype A1A2. You could choose the A1 allele first and then select the A2 allele, or you could select the A2 allele

first and then the A1 allele. The formula for this genotype is 2pq = 2(0.57)(0.43) = 0.49. You should be able to

figure out the basis for the formula.

6 Check your answer. Because there are only three possible genotypes, the sum of all the frequencies should

equal 1: 0.32 + 0.18 + 0.49 = 0.99 ≅ 1.

Practice Problems 1. The researchers mentioned in the sample problem also measured the frequency of the

alleles for the pfcrt gene in Papua New Guinea. The frequency of the K76T allele was 0.94. Assume that there is only one other allele in the population (which would have a frequency of 0.06). Use the H-W model to calculate the expected genotype frequencies in the diploid phase of the life cycle in the next generation.

2. In Malawi in 1992, the frequency of the K76T allele in P. falciparum was 0.85. a. If the assumptions of the H-W model were true, what frequency would you expect

for this allele in the year 2000? The country stopped using the drug CQ after 1992.b. Researchers measured the frequency of the K76T allele in 2000, and it was 0.13.

Which assumption of the H-W model was most likely not true?

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.3 (page 3)

3. G6PD deficiency in humans is an X-linked trait, and the H-W model can be adjusted to analyze X-linked traits. However, to practice using the H-W model, let’s assume that it functions like an autosome. In some human populations in Africa, the frequency of the A− allele is 0.25. You explored this allele in Lesson 2. Assume there is only one other al-lele in this population (frequency = 0.75). Use the H-W model to calculate the expected genotype frequencies in the next generation.

4. You examine another group of people in the Mediterranean and measure a frequency of 0.20 for the Med allele for G6PD. Because Med is recessive, we use the symbol (g) for the allele. The frequency of the alternative allele (G) is 0.80.

a. Calculate the expected genotype frequencies for the next generation. b. Suppose you measured the frequency of each genotype and found the following

results: GG = 0.50, Gg = 0.40, gg = 0.10. How could you explain these results?

5. The frequency of the A− allele in northern Europeans is very low compared to the fre-quency in some Africans. However, the vast majority of alleles for genes studied in Euro-peans and Africans are similar. One gene in both groups has two alleles. The frequency of allele 1 was 0.76 and of allele 2 was 0.24. Use the H-W model to calculate the expected genotype frequencies in the next generation.

6. What do you think it means that Europeans and Africans have very similar allele frequen-cies for most genes?

Situation 2You should be able to examine a table of genotypes and calculate the allele frequencies and the geno-type frequencies, and then predict the allele and genotype frequencies of the next generation.

Sample ProblemAnother gene that affects humans’ ability to survive malaria codes for one of the subunits of hemo-globin (the β subunit). The gene is called hemoglobin, beta (HBB). The “A” allele codes for a typical β subunit. The S allele has a mutation. If an individual has two copies of the S allele, then the person has the serious disease sickle cell anemia. You collected genotype data for 10 individuals in a group of people in sub-Saharan Africa. Use the data in Table 1 to calculate the allele and geno-type frequencies of the population, and then predict the allele and genotype frequencies of the next generation.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.3 (page 4)

Table 1.

Number Genotype

1 AA

2 SS

3 AA

4 AS

5 AA

6 AS

7 AA

8 AA

9 AA

10 AA

Step What you need to do

1 Define what is known. In this case, you can calculate the genotype frequencies directly.

2 Calculate the genotype frequencies.

frequency of A1A1 = frequency of AA = 7/10 total = 0.7

frequency of A1A2 = frequency of AS = ____________ You fill in.

frequency of A2A2 = frequency of SS = ____________ You fill in.

3 Calculate the allele frequencies. To calculate the frequency of A1, simply count the number of A alleles and divide

by the total number of alleles = 16/20 total alleles = 0.8 = p. You should repeat the calculation for the S or A2 allele

to calculate q.

Another way to get the same answer is to use the following formulas.

NA1A1 = number of individuals who are homozygous for A1,

NA1A2 = number of individuals who are heterozygous,

NA2A2 = number of individuals who are homozygous for A2,

N = total number of individuals

p = (2(NA1A1) + (NA1A2

))/N,

q = (2(NA2A2) + (NA1A2

))/N

4 Check your answer. The sum of p + q = 1. Check your answer to be sure.

5 Use what you already know. Now that you have solved for the allele frequencies, you can use the table for Situa-

tion 2 to calculate the expected frequencies of the three possible genotypes in the next generation.

Did you calculate an expected frequency for AA = 0.64, AS = .32, SS = 0.04?

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.3 (page 5)

Practice Problem7. Some people make the enzyme lactase throughout their lives, which enables them to digest

the lactose sugar found in milk and other dairy products. One dominant allele (A) that scientists have identified results in lactase being formed throughout life. A second allele (a) causes lactase production to stop after the infant stops drinking its mother’s milk. You collected genotype samples in two groups of people, southern Europeans and northern Europeans.

a. Use the data in Tables 2 and 3 to calculate the allele and genotype frequencies of the two populations.

b. Predict the genotype frequencies of the next generation.c. Describe your ideas for why the allele frequencies are different in each group.

Table 2.

Southern Europeans

Number Genotype

1 Aa

2 aa

3 Aa

4 aa

5 aa

6 Aa

7 aa

8 AA

9 aa

10 aa

Table 3.

Northern Europeans

Number Genotype

1 AA

2 aa

3 AA

4 Aa

5 Aa

6 AA

7 AA

8 Aa

9 AA

10 AA

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 3.4

a simulation tracking allele

Frequency over time

Figure 1. Screen shot from PopG showing the variables that students can change in the model. Source: PopG Genetic Simulation Program.

Table 1. Summary of the variables in the model.

Variable Comments

Population size The simulation can accept population sizes between 1 and 10,000.

Fitness of the 3 genotypes A fitness of 0 means that a specific genotype leaves no offspring. Typical values range

from 0 to 2. Under a scenario of no selection, set all the fitness values to 1.

Mutation The rate can vary from 0 to 1.

Migration rate The mutation rate is the fraction of individuals who move between populations per

generation (0 to 0.9).

Initial frequency of the A allele Values range from 0 to 1.

Generations Large numbers of generations are possible, but it takes awhile for the simulation to

complete.

Number of populations From 1 to 200 populations may be monitored simultaneously.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.1

Malaria’s effect on humans rubric

Table 1.

Task High performance Medium performance Low performance

Describe how the gene

affects the phenotype of an

individual.

Explanation is fully devel-

oped, clear, and correct.

(3 points)

Explanation is somewhat

developed or not completely

clear. (2 points)

Explanation is poorly devel-

oped or is mostly incorrect.

(1 point)

Describe how the product

of the gene may protect

against malaria.



(3 points)



clear. (2 points)



(1 point)

Describe any possible side

effects of having certain

alleles.



(3 points)



clear. (2 points)



(1 point)

Summarize simulations

to explore whether or not

certain observed allele fre-

quencies could have arisen

in a population by chance or

by natural selection.

Simulations were conducted

properly, and the results are

presented accurately and

effectively. (9 points)

Some aspects of the

simulations were completed

properly, but some aspects

were not or the results

are not well organized. (6

points)

Major errors were made in

the way the simulation was

conducted, or the results

are interpreted incorrectly.

(3 points)

Write at least 1 Hardy-Wein-

berg problem using the

gene you are studying as an

example.

Problem is relevant and

provides useful practice.

Answer provided is correct.

(3 points)

Problem is mostly relevant

and provides some practice.

Answer provided is correct.

(2 points)

Problem is not relevant,

or mistakes exist in the

answer. (1 point)

Write a full explanation for

how natural selection could

explain how populations

with extreme allele frequen-

cies evolved over time.

Answer fully accounts for

all the major principles of

evolution. (6 points)

Answer mostly accounts

for the major principles of

evolution, but some answers

are not fully developed or

are incomplete. (4 points)

Answer does not account for

all the principles of evolution

or contains multiple errors.

(2 points)

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 1)

Beyond G6PD data sets

Data Set 1: Hemoglobin, Beta (HBB); S (Sickle Cell) Allele (Visit Genetics Home Reference, http://ghr.nlm.nih.gov/gene/HBB, for more information.)Red blood cells are packed with the protein hemoglobin, which plays the critical role of carrying oxygen in the circulatory system. The hemoglobin molecule is made up of four subunits, two α subunits (alpha-globin) and two β subunits (beta-globin). The HBB gene codes for beta-globin and is between nucleotide 5,225,465 and nucleotide 5,227,070 on chromosome 11.

Figure 1. Graphic of chromosome 11, showing the location of the HBB gene. Source: Image adapted from Genetics Home Reference, 2013, HBB.

One mutation to this gene forms an allele called S (sickle cell allele). The S allele was one of the first alleles to be associated with a specific disease. The A allele is the name for the allele that codes for typical beta-globin. The mutation in the S allele causes a change in just one amino acid com-pared to the A allele (the amino acid glutamic acid is replaced with the amino acid valine at posi-tion 6 in beta-globin, written as Glu6Val).

The sickle cell allele causes some red blood cells to take on an unusual sickle shape when oxygen levels are low. A smaller proportion of red blood cells of people who have the genotype AS (hetero-zygotes, also called sickle cell carriers) are sickled, but it does not cause too many health problems. There are some reports that people who are heterozygous experience some negative effects during vigorous exercise, which explains why the National Collegiate Athletic Association requires man-datory testing of Division 1 athletes for sickle cell carrier status. Interestingly, heterozygotes have a 10-fold reduced risk of severe malaria and a much-reduced chance of death from malaria. Evi-dence supports different mechanisms to explain why AS individuals are protected, including slower growth rates of the malaria parasites in sickled cells.

http://ghr.nlm.nih.gov/gene/HBB

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 2)

People with genotype SS have sickle cell disease. Before modern medicine, sickle cell disease was debilitating and caused early death (a fitness of zero). With regular access to modern health care, people with sickle cell anemia can live with reasonably good health.

In some groups of people in sub-Saharan Africa, Greece, and India, the frequency of the S allele is up to 0.2. Data suggest that this allele evolved at least five times independently in different groups of people. A study in 2008 estimated that the S allele is between 250 and 700 years old (Modiano et al., 2008).

ReferenceModiano, D., Bancone, G., Ciminelli, B. M., Pompei, F., Blot, I., Simporé, J., & Modiano, G. (2008). Haemoglobin S

and haemoglobin C: ‘Quick but costly’ versus ‘slow but gratis’ genetic adaptations to Plasmodium falciparum malaria. Human Molecular Genetics, 17(6), 789–799.

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 3)


Data Set 2: Hemoglobin, Beta (HBB); C Allele(Visit Genetics Home Reference, http://ghr.nlm.nih.gov/gene/HBB, for more information.)Red blood cells are packed with the protein hemoglobin, which plays the critical role of carrying oxygen in the circulatory system. The hemoglobin molecule is made up of four subunits, two α subunits (alpha-globin) and two β subunits (beta-globin). The HBB gene codes for beta-globin and is between nucleotide 5,225,465 and nucleotide 5,227,070 on chromosome 11.


One particular mutation to this gene forms an allele called C. The A allele is the name for the allele that codes for typical beta-globin. The mutation in the C allele causes a change in just one amino acid compared to the A allele (the amino acid glutamic acid is replaced with the amino acid lysine at position 6 in beta-globin, written as Glu6Lys). The change in C is in the same amino acid posi-tion as S, but the replacement is a lysine, not a valine.

People with the genotype AC (heterozygotes) do not seem to suffer any ill effects. People who are homozygous CC may have very mild anemia, but many show no effects. Both heterozygotes AC and homozygotes CC are protected from Plasmodium falciparum malaria, possibly because infected red blood cells are more easily destroyed by the immune system.

The C allele is not widespread, but it reaches a frequency of 0.5 in the Ivory Coast, a country in West Africa. A study in 2008 estimated that the C allele is between 950 and 3000 years old (Modi-ano et al., 2008).

ReferenceModiano, D., Bancone, G., Ciminelli, B. M., Pompei, F., Blot, I., Simporé, J., & Modiano, G. (2008). Haemoglobin S

and haemoglobin C: ‘Quick but costly’ versus ‘slow but gratis’ genetic adaptations to Plasmodium falciparum malaria. Human Molecular Genetics, 17(6), 789–799.


Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 4)


Data Set 3: Hemoglobin, Beta (HBB); E Allele(Visit Genetics Home Reference, http://ghr.nlm.nih.gov/gene/HBB, for more information.)Red blood cells are packed with the protein hemoglobin, which plays the critical role of carrying oxygen in the circulatory system. The hemoglobin molecule is made up of four subunits, two α subunits (alpha-globin) and two β subunits (beta-globin). The HBB gene codes for beta-globin and is between nucleotide 5,225,465 and nucleotide 5,227,070 on chromosome 11.


One particular mutation to this gene forms an allele called E. The A allele is the name for the allele that codes for typical beta-globin. The mutation in the E allele causes a change in just one amino acid compared to the A allele (the amino acid glutamic acid is replaced with the amino acid lysine at position 26 in beta-globin, written as Glu26Lys).

The messenger RNA (mRNA) formed from the E allele is processed differently, so fewer beta-glo-bin molecules are made and the beta-globin molecules that are formed are structurally deficient. People who are homozygous EE have a mild form of a disease called thalassemia. People who are heterozygous (AE) do not show any ill effects. The red blood cells of heterozygotes AE seem to be protected from being invaded by Plasmodium falciparum.

The E allele is the most common variant allele of HBB in Southeast Asia. In some areas of Thailand and Cambodia, the frequency is up to 0.70. A study in 2004 estimated that the E allele is between 1550 and 5550 years old (Ohashi et al., 2004).

ReferenceOhashi, J., Naka, I., Patarapotikul, J., Hananantachai, H., Brittenham, G., Looareesuwan, S., . . . Tokunaga, K.

(2004). Extended linkage disequilibrium surrounding the hemoglobin E variant due to malarial selection. The American Journal of Human Genetics, 74(6), 1198–1208.


Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 5)


Data Set 4: Major Histocompatibility Complex, Class I, B (HLA-B); Allele HLA-B53(Visit Genetics Home Reference, http://ghr.nlm.nih.gov/gene/HLA-B, for more information.)The protein from the HLA-B gene plays a critical role in the immune system. As a part of the human leukocyte antigen complex, the protein from HLA-B helps the immune system tell the dif-ference between proteins from foreign invaders like bacteria or viruses and the body’s own proteins. There are hundreds of different alleles for HLA-B, and each is assigned its own number. HLA-B spans from nucleotide 31,353,867 to nucleotide 31,357,211 on chromosome 6.

Figure 4. Graphic of chromosome 6, showing the location of the HLA-B gene. Source: Image adapted from Genetics Home Reference, 2013, HLA-B.

The allele HLA-B53 is associated with a decreased risk of severe malaria in both homozygotes and heterozygotes, presumably because it increases the immune system’s ability to identify and destroy Plasmodium falciparum–infected cells. The frequency of this allele is high in sub-Saharan Africa, and is up to 40 percent in Nigeria. A study in 2011 suggested that this allele was approximately 2150 years old. There appear to be no side effects of being homozygous or heterozygous for this allele (Hedrick, 2011).

ReferenceHedrick, P. W. (2011). Population genetics of malaria resistance in humans. Heredity, 107(4), 283–304.

http://ghr.nlm.nih.gov/gene/HLA-B

Malaria

© 2

015

Smit

hson

ian

Inst

itut

ion.

Per

mis

sion

to c

opy

and

dist

ribu

te is

free

ly g

rant

ed fo

r ed

ucat

iona

l, no

ncom

mer

cial

use

onl

y.

Master 4.2 (page 6)


Data Set 5: Atypical Chemokine Receptor 1 (ACKR1), Duffy Blood Group, Chemokine Receptor (DARC); FYB-Erythroid Silent (ES) or Duffy “Null” Allele (Visit Genetics Home Reference, http://ghr.nlm.nih.gov/gene/ACKR1, for more information.)Like the ABO blood type system, red blood cells and other cells make another glycoprotein that also can cause an immune system response. In the Duffy blood group system, the FYA and FYB alleles of the ACKR1 gene code for the Fya and Fyb antigens, respectively. ACKR1 spans from nucleotide 159,204,012 to nucleotide 159,206,499 on chromosome 1. Another allele called FYB-erythroid silent (ES) or Duffy “null” results in no antigens being formed in red blood cells. The FYB-ES allele in Africa has a C instead of a T 33 nucleotides away from the site where tran-scription begins on the FYB allele. This change blocks the expression of the gene.

Figure 5. Graphic of chromosome 1, showing the location of the ACKR1 gene. Source: Image adapted from Genetics Home Reference, 2013, ACKR1.

People who are homozygous for the ES allele are able to completely resist infection from another species of Plasmodium that can cause a different form of malaria: P. vivax. However, this allele does not protect against infection from P. falciparum.

In some areas of sub-Saharan Africa, the frequency of the ES allele is 100 percent. Outside of Africa, this allele is very rare (<1 percent). A study in 2002 suggested that the ES allele is between 4250 and 26,500 years old (Seixas, Ferrand, & Rocha, 2002).

ReferenceSeixas, S., Ferrand, N., & Rocha, J. (2002). Microsatellite variation and evolution of the human Duffy blood group

polymorphism. Molecular Biology and Evolution, 19(10), 1802–1806.

http://ghr.nlm.nih.gov/gene/ackr1

Malariacredits

86

credits

Cover: Source: “Mosquito” ©iStock.com/Christopher Badzioch

Lesson 1: Changes in a Long-Term RelationshipMaster 1.1. Figure 1. Source: Centers for Disease Control and Prevention. (2012). CDC malaria map application [Interactive map]. Retrieved from http://cdc-malaria.ncsa.uiuc.edu/.

Master 1.3. Figure 1. Source: Adam Cole. (2012). Herbs and empires: A brief, animated history of malaria drugs [Screen shots from video]. NPR. Retrieved from http://www.npr.org/blogs/health/2012/12/13/167188333/herbs-and-empires-a-brief-animated-history-of-malaria-drugs.

Master 1.6. Source: Ecker, A., Lehane, A. M., Clain, J., & Fidock, D. A. (2012). PfCRT and its role in antimalarial drug resis-tance. Trends in Parasitology, 28(11), 504–514.

Master 1.7. Table 1. Source: Fidock, D. A., Nomura, T., Talley, A. K., Cooper, R. A., Dzekunov, S. M., Ferdig, M. T., Ursos, L. M. B., Sidhu A. B. S., Naudé, B., Deitsch, K. W., Su, X.-z., Wootton, J. C., Roepe, P. D., & Wellems, T. E. (2000). Mutations in the P. falciparum digestive vacuole transmembrane protein PfCRT and evidence for their role in chloroquine resistance. Molecular Cell, 6(4), 861–871. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944663/table/T1/; Figure 2. Source: Data from Sidhu, A. B. S., Verdier-Pinard, D., & Fidock, D. A. (2002). Chloroquine resistance in Plasmodium falciparum malaria parasites conferred by pfcrt mutations. Science, 298(5591), 210–213; Table 2. Data from Manske, M., Miotto, O., Campino, S., Auburn, S., Almagro-Garcia, J., Maslen, G., . . . Rayner, J. C. (2012). Analysis of Plasmodium falciparum diversity in natural infections by deep sequencing. Nature, 487(7407), 375–379; Table 3. Data from Kublin, J. G., Cortese, J. F., Njunju, E. M., Mukadam, R. A. G., Wirima, J. J., Kazembe, P. N., . . . Plowe, C. V. (2003). Reemergence of chloroquine-sensitive Plasmodium falciparum malaria after cessation of chloroquine use in Malawi. Journal of Infectious Diseases, 187(12), 1870–1875, and Laufer, M. K., Takala-Har-rison, S., Dzinjalamala, F. K., Stine, O. C., Taylor, T. E., & Plowe, C. V. (2010). Return of chloroquine-susceptible falciparum malaria in Malawi was a reexpansion of diverse susceptible parasites. Journal of Infectious Diseases, 202(5), 801–808.

Lesson 2: Malaria and Human DiversityMaster 2.1. Figure 1. Source: Beutler, E. (2008). Glucose-6-phosphate dehydrogenase deficiency: A historical perspective. Blood, 111, 16–24; Figure 2. Source: Beutler, E. (2008). Glucose-6-phosphate dehydrogenase deficiency: A historical perspective. Blood, 111, 16–24; Figure 3. Source: Frank, J. E. (2005). Diagnosis and management of G6PD deficiency. American Family Physician, 72(7), 1277–1282. Retrieved from http://www.aafp.org/afp/2005/1001/p1277.html.

Master 2.2. Figures 1 and 2. Source: Howes, R. E., Piel, F. B., Patil, A. P., Nyangiri, O. A., Gething, P. W., Dewi, M., Hogg, M. M., Battle, K. E., Padilla, C. D., Baird, J. K., & Hay, S. I. I. (2012). G6PD deficiency prevalence and estimates of affected popu-lations in malaria endemic countries: A geostatistical model-based map. PLOS Medicine, 9(11), e1001339. doi:10.1371/journal.pmed.1001339. Retrieved from http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001339.

Master 2.3. Figure 2. Source: Images adapted from (top) Genetics Home Reference. (2013). G6PD. Retrieved from http://ghr.nlm.nih.gov/gene/G6PD; (bottom) Cappellini, M. D., & Fiorelli, G. (2008). Glucose-6-phosphate dehydrogenase deficiency. Lancet, 371, 64–74; Table 1. Source: Tishkoff, S. A., & Verrelli, B. C. (2004). G6PD deficiency and malarial resistance in humans: Insights from evolutionary genetic analyses. Infectious Disease and Host-Pathogen Evolution, 39–74.

Lesson 3: Malaria and Population GeneticsMaster 3.4. Figure 1. Screen shot from PopG Genetic Simulation Program. Retrieved from http://evolution.gs.washington.edu/popgen/popg.html.

Lesson 4: Beyond G6PDMaster 4.2. Figure 1. Source: Image adapted from Genetics Home Reference. (2013). HBB. Retrieved from http://ghr.nlm.nih.gov/gene/HBB; Figure 2. Source: Image adapted from Genetics Home Reference. (2013). HBB. Retrieved from http://ghr.nlm.nih.gov/gene/HBB; Figure 3. Source: Image adapted from Genetics Home Reference. (2013). HBB. Retrieved from http://ghr.nlm.nih.gov/gene/HBB; Figure 4. Source: Image adapted from Genetics Home Reference. (2013). HLA-B. Retrieved from http://ghr.nlm.nih.gov/gene/HLA-B; Figure 5. Source: Image adapted from Genetics Home Reference. (2013). ACKR1. Retrieved from http://ghr.nlm.nih.gov/gene/ACKR1.

http://cdc-malaria.ncsa.uiuc.edu/



http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944663/table/T1/

http://www.aafp.org/afp/2005/1001/p1277.html

http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001339

http://ghr.nlm.nih.gov/gene/G6PD

http://ghr.nlm.nih.gov/gene/G6PD











http://ghr.nlm.nih.gov/gene/ACKR1

http://ghr.nlm.nih.gov/gene/ACKR1

Documents

Developed as a Part of the - Human Evolution by The ...humanorigins.si.edu/sites/default/files/Teachers... · Malaria teacher guide Developed as a Part of the Teaching Evolution through