By Cynthia Cheung and Preeti Sharma

Teaching the Concept ofMECHANISM OF EVOLUTION

Introduction to mechanism of evolutionYou may know what evolution is (that is, the process of change over time), but you may wonder about how or why evolution occurs.

In this presentation, two main questions will be addressed:• How does evolution occur? • Why do organisms evolve?

By examining the mechanisms of evolution, these questions will be answered.

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Lesson Sequence1. Genetic variation2. Natural selection3. Sexual selection4. Genetic drift5. Applications and societal implications

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Curriculum expectations addressed: (Gr. 11 SBI3U)C1.1 Evaluate the possible impact of an environmental change on natural selection and on vulnerability of species. C2.1 Use appropriate terminology related to evolution, including but not limited to extinction, natural selection, phylogeny, speciation, niche, mutation, mimicry, adaptation and survival to the fittestC3.1 Explain the fundamental theory of evolution, using the evolutionary mechanism of natural selection to illustrate the process of biological change over timeC3.4 describe some evolutionary mechanisms, and explain how they affect the evolutionary development and extinction of various species

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Diagnostic assessment

Assessment for learning:

Do students understand evolution?

What misconceptions do students have?

What do they know already about the mechanisms of evolution?

Sample anticipation guide statements: Evolution is about progression of

organisms from simple to complex. Evolution can occur in individuals. Natural selection chooses only the best

organisms to survive. There is more than one way to explain

evolution.

Students rate these statements ranging from strongly disagree to strongly agree (scale of 1 to 5). Discussion may follow, or teachers may collect assessments to inform future instruction.

Genetic variation is the basis of mechanisms of evolution

Without genetic variation, mechanisms would not occur

There are three primary sources of genetic variationMutationsGene flowSex

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Important to remember…

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Mutations are random

Can be beneficial, neutral or harmful to organism

Mutations can occur in any cell of an organism

Somatic mutations occur in non-reproductive cells and won’t be passed on to offspring

Only mutations in reproductive cells will impact offspring and populations

For example, the different colouration of this apple is caused by a mutation in a somatic cell. Therefore, the seeds of this apple will not carry the mutation.

Lesson 1 – Genetic Variation - MutationsNot all mutations matter to evolution

Definition:Mutations are changes in an organism’s DNA. These changes affect all aspects of the organism’s life.

Mutations

Sex

Gene flow

Gene Flow

Mutations

Sex

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Lesson 1 – Genetic Variation – Gene flow

Two Sub-populations of Beetles

• Movement of genes from one population to another through migration

• Leads to the transfer of genes

• Changes the frequency of genes in original and new populations

Teaching idea: Gene flow role play• Students are randomly divided in two groups with

different colour caps (or pinnies, or buttons) and are separated into two groups in the classroom.

• Each coloured group denotes a population.• Students are instructed to either stay in their

current population or move to the other population.

• Give them three opportunities to move or stay

• After activity, discuss:• How did the populations change?• What factors made you want to stay or move?• What factors may play a part in determining

gene flow in nature? (e.g., physical barriers, resources like food, shelter, mating opportunity)

Gene Flow

Mutations

Sex

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Lesson 1 – Genetic Variation – Gene flow

Mutations

Sex

Genetic shuffling results when two organisms undergo sexual reproduction

New combinations of genes are introduced

Introduces genetic variation

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Lesson 1 – Genetic Variation – Sex

Gene flow

Assessment for, of learning at end of lesson - students complete an exit slip and hand in as they leave:

Exit Slip• 3 key things I learned

today:

• 2 things I found interesting:

• 1 question I still have:

Video to introduce concept: Hummingbirds in Ecuador

Before video: Ecuador is home to over 132 species of

hummingbirds Pose questions to focus learning:

How did such diversity in hummingbirds arise?

What mechanisms do the scientists in the video explain this diversity?

What are the four processes involved? What features of hummingbirds are affected

because of their environment? During video (click image to the right to

open video): Students answer questions and take notes

After video briefly discuss answers as a whole class

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Lesson 2 – Natural selection

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Lesson 2 – Natural selectionTeaching idea: Clipbirds

A hands-on activity to simulate evolution of beak sizes in birds

Beak sizes are simulated using clips of different sizesStudents carry out simulation where food availability

varies from season to seasonStudents analyze results of activity and make

connections to how natural selection affects bird beak size in natural populations

Full lesson plan can be found at http://www.ucmp.berkeley.edu/education/lessons/clipbirds/

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Lesson 2 – Natural selectionAssessment for, of learning: Individual

case studyStudents choose a short film to watch from

http://hhmi.com/biointeractive/shortfilms/ Each film focuses on a different example of

natural selectionStudents will hand in a written summary

that addresses:How natural selection affected their particular

speciesWhat adaptations have resultedHow the environment affected the evolution of

the species

Activating prior knowledge: What do you think “survival of the fittest” means?Students write responses down on a slip of

paper and hand in to teacherTeacher reads responses out loud, without

judgementStudents will revisit their response after

viewing following comic strip

Misconceptions identified here and from the diagnostic assessment can be addressed during this activity

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Lesson 3 – Sexual selection

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Discussion questions• When it comes to crickets, what does

fitness mean?• Is calling good or bad for a cricket's

fitness?• Give some examples of selection at

work in this cricket story.• How does selection favour calling? • How does selection favour not

calling?

Student self reflection – how has your understanding of “fitness” changed?

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Question: If a cricket’s call attracts predators, why do they still do it? Wouldn’t natural selection select for individuals that don’t call?Introduce concept of sexual selection as

another mechanism of evolutionExplains why some species of animals exhibit

adaptations that jeopardize survival

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Lesson 3 – Sexual selection

Why do male peacocks continue to display large and colourful plumage even though it may be harmful to its survival?

Online simulation – Exploring sexual selection in guppies (individual student activity)Why are guppies so colourful?

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Lesson 3 – Sexual selection

Click on image to go to website

Not all sexually selected traits are harmful to organisms

Guest Lecturer video: In fruit flies,

wings show great diversity in patterns

Sexual selection acts to select for individuals with spotted wings

Click image to watch video – excerpt is from part 10-14

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Lesson 3 – Sexual selection

A change in a small and isolated population that

takes place strictly by chance is referred to as genetic drift.

It is random and accidental. The resulting change may provide no

survival advantage for the organism.

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Lesson 4 – Genetic drift

Assessment: Compare and contrast genetic drift with natural selection using a Venn diagram

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Lesson 4 – Genetic drift

Natural selection

Genetic drift

Need an extension for enriched students? Have them complete a Venn diagram that compares natural selection, genetic drift and sexual selection!

Artificial selection:By farmers for

desired traits in plants and crops (e.g., organic farming)

Animal breeding (e.g., dogs, horses)

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Lesson 5 – Application and societal implications

Artificial selection cont’d:Genetic engineering (e.g., antibiotic resistance genes, DNA

manipulation)Used to evolve proteins with particular properties, such as

modified enzymes or new antibodies.

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Lesson 5 – Application and societal implications

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Lesson 5 – Application and societal implicationsMedicine

Research into evolution of antibiotic-resistant bacteria

Understanding genes responsible for disorders For example: the Mexican tetra fish

diagnostic assessment - anticipation guide exit slips to assess learning during teacher-led instruction (K/U)graphic organizers to summarize learning (K/U, T/I) lab reports (e.g., Clipbirds, guppy simulation) (K/U, T/I, C)Case study (e.g., natural selection) (K/U, A)Discussions (K/U, C)

As a summative task, students are asked to answer the question: how do evolutionary mechanisms affect my life? They will research a topic (an application or societal implication) and present their answer using one of the following methods : Poster (traditional form, or electronic using Glogster) written lab report role-play/drama/ video Powerpoint or Prezi presentation lyrics and song

Evaluation of summative task will address the following achievement chart categories (T/I, C, A) 25

Assessments

Kinesthetic learners will benefit from the hands-on activities and virtual labs

Auditory learners will benefit from videos and mini-lectures

Visual learners will benefit from videos

Activities vary from whole class (e.g., discussions) to small groups (e.g.,

Clipbirds lab), to individual (e.g., online simulation)groupings can be altered to suit class needs

Assessments varyStudent choice allowed where possibleSummative task allows choice based on interest and

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Differentiated instruction

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Accommodations Students with IEP’s:

accommodate according to IEP strategies and methods provide additional time, extra support where needed

Students that are ELL’s: provide graphic organizers to take notes pair up with another student that speaks first language pre-teach vocabulary by providing a glossary of key terms

ahead of lesson allow use of electronic dictionaries or online translation tools use visual representations where possible to explain concepts

Enriched students: allow independent study projects in a topic that interests them independently find other examples of mechanisms at work and

share with class/teacher provide extensions to class activities

Misconceptions about natural selection, especially about phrase “survival of the fittest”See lesson 3 for details to address possible misconceptions

Students may find it difficult to understand the difference between somatic or genetic variation and why the latter is responsible for evolution.Emphasize this point when teaching about mutations

Some students may object to the topic of evolution because it is incompatible with their religious faith. send home a letter before unit; open up communication with

parentsemphasize that evolution is a scientific theory that serves to

explain observations we see in the natural worldmay need to consult with head of department or admin if

student refuses to participate in learning 28

Possible student difficulties and solutions

For summarizing key ideas could be provided at the beginning of the unit to provide a big picture of

the unit. as learning occurs, students can fill in the blank spaces with key ideas of

that subtopic. could also be used at the end of a unit to summarize and review key ideas

of the unit.

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Sample graphic organizer

This can be differentiated for students in the following ways:• enriched

students create organizer on their own;

• include more pictures for ELL’s;

• provide a completed copy for students with learning needs

Farabee, M.J. (2001). Development of Evolutionary Theory. Retrieved July 17, 2012, from http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEVOLI.html

An online source for concepts in evolution.

Howard Hughes Medical Institute. (2012). Biointeractive - Evolution. Retrieved July 17, 2012, from http://www.hhmi.org/biointeractive/evolution/index.html

A collection of videos (lecturers, animations) and articles about evolution.

University of California Museum of Paleontology. (2012). How does evolution impact my life? Retrieved July 17, 2012, from http://evolution.berkeley.edu/evolibrary/search/topicbrowse2.php?topic_id=47

 A list of resources and topics for applications and societal implications.

University of California Museum of Paleontology. (2012). Understanding Evolution. Retrieved July 17, 2012, from http://evolution.berkeley.edu/evolibrary/teach/index.php

A comprehensive website that provides a deep conceptual understanding of evolution, as well as teaching strategies, common misconceptions, and tons of resources (e.g., image library, teaching materials database).

WGBH Educational Foundation and Clear Blue Sky Productions, Inc. (2011). Evolution library. Retrieved July 17, 2012, from http://www.pbs.org/wgbh/evolution/library/index.html

A set of resources including books, articles, links and images related to topics in evolution. 30

References and sources