Chapter 13: Genetic Technology Text...tinue to impact every aspect of your life, from growing the food you eat to treating a dis-ease you might inherit. Genetic Technology in Our Lives

Activities/FeaturesObjectivesSection

Chapter 13 OrganizerChapter 13 Organizer

Applied GeneticsNational Science EducationStandards UCP.2, UCP.3;A.1, A.2; C.2; E.1, E.2; F.1;G.1-3 (1 session)

Recombinant DNATechnologyNational Science EducationStandards UCP.2, UCP.3,UCP.5; A.1, A.2; C.2; E.1,E.2; F.1, F.4, F.5, F.6; G.1, G.2(2 sessions)

The Human GenomeNational Science EducationStandards UCP.2, UCP.3;A.1, A.2; C.2; E.1, E.2; F.1,F.6; G.1-3 (2 sessions)

1. Predict the outcome of a test cross.2. Evaluate the importance of plant and

animal breeding to humans.

3. Summarize the steps used to engineertransgenic organisms.

4. Give examples of applications and benefits of genetic engineering.

5. Analyze how the effort to completelymap and sequence the human genomewill advance human knowledge.

6. Predict future applications of theHuman Genome Project.

Focus On Selective Breeding of Cats, p. 344Problem-Solving Lab 13-1, p. 347

MiniLab 13-1: Matching Restriction Enzymesto Cleavage Sites, p. 351Inside Story: Gel Electrophoresis, p. 354Problem-Solving Lab 13-2, p. 355Investigate BioLab: Modeling RecombinantDNA, p. 362BioTechnology: How to Clone a Mammal,p.364

MiniLab 13-2: Storing the Human Genome,p. 358Careers in Biology: Forensic Analyst, p. 359Problem-Solving Lab 13-3, p. 361

MATERIALS LIST

BioLabp. 362 paper, transparent tape, scis-sors, red and green pencils

MiniLabsp. 351 paper, pencilp. 358 paper, pencil, book, calculator(optional)

Alternative Labp. 358 microscope, microscope slide,prepared slide of female cheek cells, T-shirt, red ink, red grape juice, humanhair (blond and dark), envelopes (4),bar codes (5)

Quick Demosp. 346 photographs of petsp. 350 Chromosome Simulation Biokitp. 359 human chromosome map

Need Materials? Contact Carolina Biological Supply Company at 1-800-334-5551or at http://www.carolina.com

Products Available From NationalGeographic SocietyTo order the following products, call NationalGeographic Society at 1-800-368-2728:VideoDNA: Laboratory of Life

Teacher’s Corner

342B342A

Genetic TechnologyGenetic Technology

TransparenciesReproducible MastersSection

Applied Genetics

Recombinant DNATechnology

The HumanGenome

Section 13.1

Section 13.2

Section 13.3

Teacher Classroom Resources

Reinforcement and Study Guide, p. 55Laboratory Manual, pp. 91-94Content Mastery, pp. 61, 64

Reinforcement and Study Guide, pp. 56-57BioLab and MiniLab Worksheets, pp. 61-62Laboratory Manual, pp. 95-98Tech Prep Applications, pp. 21-22Content Mastery, pp. 61-62, 64

Reinforcement and Study Guide, p. 58Concept Mapping, p. 13Critical Thinking/Problem Solving, p. 13BioLab and MiniLab Worksheets, pp. 63-66Content Mastery, pp. 61, 63-64Tech Prep Applications, pp. 21-22 L2

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Section Focus Transparency 32Basic Concepts Transparency 19

Section Focus Transparency 33Reteaching Skills Transparency 22

Section Focus Transparency 34

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Assessment Resources Additional ResourcesSpanish ResourcesEnglish/Spanish AudiocassettesCooperative Learning in the Science ClassroomLesson Plans/Block Scheduling

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Chapter Assessment, pp. 73-78MindJogger VideoquizzesPerformance Assessment in the Biology ClassroomAlternate Assessment in the Science ClassroomComputer Test BankBDOL Interactive CD-ROM, Chapter 13 quiz

Section 13.2

Section 13.1

Section 13.3

Refer to pages 4T-5T of the Teacher Guide for an explanation of the National Science Education Standards correlations.

Key to Teaching StrategiesKey to Teaching Strategies

Level 1 activities should be appropriatefor students with learning difficulties.Level 2 activities should be within theability range of all students.Level 3 activities are designed for above-average students.ELL activities should be within the abilityrange of English Language Learners.

Cooperative Learning activitiesare designed for small group work.These strategies represent student prod-ucts that can be placed into a best-workportfolio.These strategies are useful in a blockscheduling format.

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The following multimedia resources are available from Glencoe.

Biology: The Dynamics of LifeCD-ROM

Animation: Gene CloningVideo: BioengineeringAnimation: Recombinant DNA

Videodisc ProgramGene CloningBioengineeringRecombinant DNA

The Infinite VoyageThe Geometry of LifeTestcross–HomozygousTestcross–HeterozygousMiracles by Design

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http://www.carolina.com

Section

Selective Breeding The same principle of selective

breeding that applies to cats alsoapplies to much of the food we eatand to the animals such as horses thathelp us with hard labor. You can readabout the selective breeding ofdomesticated cats in the Focus On fea-ture on the next page. The process ofselective breeding requires time,patience, and several generations ofoffspring before the desired traitbecomes common in a population.Although our ancestors did not real-ize it, their efforts at selective breed-ing increased the frequency of adesired allele within a population.Increasing the frequency of desired

alleles in a population is the essenceof genetic technology.

Selective breeding producesorganisms with desired traits

From ancient times, breeders havechosen the plants and animals withthe most desired traits to serve asparents of the next generation.Farmers use for seed the largestheads of grain, the juiciest berries,and the most disease-resistant clover.They raise the calves of the best milkproducer and save the eggs of thebest egg-laying hen for hatching.Breeders of plants and animals wantto be sure that their populationsbreed consistently so that each mem-ber shows the desired trait.

13.1 APPLIED GENETICS 343

For thousands of years, humans haveadmired the strength, power, andgrace of animals like this mountain

lion. Through years of selective breeding,people have been able to select certain quali-ties in plants and animals and breed themso that these qualities are common andmore useful to humans. The traits of themountain lion would not be desir-able in a domesticated cat.Instead, gentleness and theability to provide compan-ionship are traits thathave been selectively bredinto these pets.

SECTION PREVIEW

ObjectivesPredict the outcome of a test cross.Evaluate the impor-tance of plant and animal breeding tohumans.

Vocabularyinbreedingtest cross

13.1 Applied Genetics

Mountain lion (above) anddomesticated cat (inset)

343

Section 13.1

BIOLOGY: The Dynamics of Life SECTION FOCUS TRANSPARENCIES

Use with Chapter 13,Section 13.1

What are some desired traits that breeders might want to selectfor in these food sources?

What would breeders need to know about each trait to producethe desired trait in offspring?

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PrepareKey ConceptsStudents will study the role of the test cross as a tool in deter-mining genotypes. They investi-gate means of achieving desirabletraits in plants and animalsthrough the practices of selectivebreeding and hybridization.

Planning■ Purchase fruits and vegetables

for the Getting Started Demo.

1 FocusBellringer Before presenting the lesson, display Section Focus Trans-parency 32 on the overhead pro-jector and have students answerthe accompanying questions.

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342 GENETIC TECHNOLOGY

Genetic Technology

What You’ll Learn■ You will evaluate the impor-

tance of plant and animalbreeding to humans.

■ You will summarize the stepsused to engineer transgenicorganisms.

■ You will analyze how map-ping the human genome willbenefit human life.

Why It’s Important Genetic technology will con-tinue to impact every aspect ofyour life, from growing thefood you eat to treating a dis-ease you might inherit.

Genetic Technology inOur LivesBring in articles from maga-zines or newspapers dealingwith such genetic technology ascloning animals or new medi-cines. Create a poster with yourarticles. What potential do yousee for genetic technology toaffect your future?

To find outmore about

genetic technology, visit theGlencoe Science Web Site.www.glencoe.com/sec/science

13

GETTING STARTEDGETTING STARTED

ChapterChapter

Genetic technology pro-vides opportunities forchanging plants and ani-mals. Dolly the sheep wasthe first cloned mammal.Strawberry plants havebeen made frost-resistantby genetic engineering.

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Theme DevelopmentThe theme of evolution is allud-ed to as students are introduced toselective breeding techniques thatachieve new and different traits inoffspring. The theme nature ofscience is developed in this chap-ter as the techniques for changingthe genetic makeup of organismsare discussed. Some of the tech-niques may be used to restorehomeostasis to organisms afflict-ed with genetic disorders.

Chapter 13Chapter 13

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Tech Prep, p. 345;Meeting Individual Needs, p. 350;

Project, p. 352; Reteach, 356; Exten-sion, p. 361; Going Further, p. 363

Visual-Spatial Portfolio, p. 345;Meeting Individual Needs, p. 345;

Quick Demo, p. 359

Intrapersonal Enrichment, p. 352Linguistic Biology Journal, pp. 346, 355, 360; Portfolio,

p. 353; Meeting Individual Needs,p. 357

GETTING STARTED DEMOGETTING STARTED DEMO

Bring in several vegetables andfruits such as corn or strawber-ries and ask how genetic tech-nology could improve them.Answers may include makingproduce larger, making thembruise less easily, or helpingthem survive adverse weatherconditions such as frost.

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If time does not permit teach-ing the entire chapter, use theBioDigest at the end of theunit as an overview.

Assessment PlannerAssessment PlannerPortfolio Assessment

Portfolio, TWE, pp. 345, 353, 360MiniLab, TWE, pp. 351, 358

Performance AssessmentAssessment, TWE, p. 353Problem-Solving Lab, TWE, p. 355Alternative Lab, TWE, pp. 358-359BioLab, TWE, pp. 362-363BioLab, SE, pp. 362-363MiniLab, SE, pp. 351, 358

Knowledge AssessmentAssessment, TWE, pp. 346, 348, 356Problem-Solving Lab, TWE, p. 360Section Assessment, SE, pp. 348, 356, 361Chapter Assessment, SE, pp. 365-367

Skill AssessmentProblem-Solving Lab, TWE, p. 347Assessment, TWE, p. 361

Resource ManagerResource Manager

Section Focus Transparency 32and Master

Tech Prep Applications,pp. 19-20 L2

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http://www.glencoe.com/sec/science

SILVER MANX TABBY(ABOVE), AND WHITE

PERSIAN GETTINGGROOMED

TRAITS AND TEMPERAMENTSSome cats have been bred for special traits. The Manx (right), for example, is tailless. Manx cats trace their roots to the Isle of Man off the coast of England. With hind legs longer than front legs, Manx cats run with a rabbitlike, hopping gait. The breed known as Ragdoll gets its name from the fact that it relaxes its muscles and goes completely limp when picked up. Fearless and calm, the Ragdoll is a fairly

new breed of cat, which originated in the United States in the 1960s. Different breeds of cats have different temperaments, or personalities. Siamese tend to be vocal and demanding. TheJapanese bobtail—thought to bring goodluck—is playful andadaptable. The elegantAbyssinian is known forbeing quiet and veryaffectionate.

SHORT VERSUS LONG Cat breeds can be divided into two major groups: those with short hairand those with long. The Abyssinian—slender and regal-looking withlarge ears and almond-shaped eyes—is a popular short-haired breed. Theancestry of Abyssinians is unclear, but they may be descended from thesacred cats of ancient Egypt. Certainly, their similarity to Egyptian catsculptures, such as the one at left, is striking. The American shorthair, on the other hand, is a sturdy muscular breed developed from cats thataccompanied European settlers to the American colonies.

There are about a dozen breeds of longhaired cats, ranging from thelarge (up to 13.5 kg, or 30 pounds), shaggy Maine coon cat to the ever-popular Persian. Persian cats (below) are prized for their extremely longfur that stands out from their bodies, especially on the neck, face, and tail. Hundreds of years of careful breeding have refined the distinct “powder puff” appearance of the modern Persian.

1 THINKING CRITICALLY The ancient Egyptians stored large amounts ofgrain near their cities to ensure there would be enough to eat when cropsfailed. Speculate on why the ancient Egyptians may have been motivatedto domesticate cats.

2 JOURNAL WRITING Research a breed of domestic cat. In your journal,write about the breed's history and specific traits for which it was bred.

EXPANDING Your View

SCULPTURE OF EGYPTIAN GODDESS BASTET AS A CAT

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Visual Learning■ Make a bulletin-board display

showing a variety of catbreeds. Have interested stu-dents research the history ofsome of these breeds.

■ Locate a local cat breeder andhave the breeder bring in a catto demonstrate how you wouldshow a cat at a cat show.

Answers to Expanding Your View

1. Grain would attract rodentsthat would also carry diseases.Cats would keep the rodentpopulation at a minimum.

2. Answers will vary dependingon the breed selected. Checkto see whether physical traitssuch as hair length or color ortemperament are mentioned.

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SelectiveGraceful, agile, and independent,cats are popular pets. In theUnited States alone, more than55 million cats are kept as pets.Although the origin of thedomestic cat is lost in antiquity,archeological evidence indicatesthat an association between catsand people existed as much as 3500 years ago in ancient Egypt.Unlike dogs, cattle, and manyother domesticated animals,however, cats have only recentlybeen bred selectively to exhibitspecific traits. Currently about 40recognized breeds exist—devel-oped by selectively mating catshaving especially desirable ordistinctive characteristics. Different breeds vary primarily in color, in length and texture of fur, and in temperament.

COLORFUL COATSCats come in many colors, butthe most common coats are tabby(a striped or blotchy pattern),black, and orange. Cats with“orange” coats range in colorfrom creamy yellow to dark gin-ger red. The genetic control ofcat fur color is complex and onlypartially understood. Solid whitefur is dominant to all other furcolors. Spots of white—especiallyon the face, throat, and paws—are also dominant to solid colorcoats. Some breeds such as theSiamese (below) have been bredfor a light-colored body with darklegs, tail, ears, and face—the per-fect frame for bright blue eyes.

FOCUS ON

Breeding ofCats

SOMALI—ALONGHAIRED

ABYSSINIANBREED—ATCAT SHOW

KITTENS (ABOVE AND BELOW) WITH DOMINANT WHITE MARKINGSON FACE, PAWS, AND THROAT

▼

SIAMESE

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2 Teach

Focus OnSelective Breeding of CatsPurpose Students will gain some insightinto the breeding of cats and theinfluence of cats on human lifethroughout history.

BackgroundCats can be bred for a number ofcharacteristics, including physicaltraits such as hair length or color.Temperament can also be selectedby breeding. Certain breeds havea reputation for being quiet andloving, others for being noisy.

Teaching Strategies■ Make sure that students arefamiliar with the meaning of theterms breed and selective breeding.■ Ask students to bring in pho-tographs of their pet cats. If anystudent’s cat is a pure breed, havethe student describe distinctivetraits or qualities of the breed.

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PortfolioPortfolio

Test CrossVisual-Spatial Have students drawPunnett squares to show: a guinea

pig of unknown genotype and normalphenotype mated with one known to behomozygous for a recessive allele, dd,which causes a bone deformity. Half theoffspring have normal bones; half havethe deformity.

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MEETING INDIVIDUAL NEEDS MEETING INDIVIDUAL NEEDS

GiftedVisual-Spatial Have students dolibrary research to determine the lin-

eage of domestic cats. They can design achart or poster that traces the taxonomyof cats and shows relatives of cats that arenot domesticated. Students will require abasic understanding of levels of classifica-tion in order to do the project. L3

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VIDEODISCThe Infinite VoyageThe Geometry of Life

Selective Breeding (Ch. 7)2 min. 30 sec.

VIDEOTAPEThe Secret of Life

Gone Before You Know It: TheBiodiversity Crisis

!7itB"

Plant BreedingKinesthetic Have studentsvisit a grocery store and

take notes and make diagramsof squash varieties. Include anyinformation the store might provide. Then, after the dia-grams and information arerecorded, advise students thatsummer squash (crookneck, custard marrow, pattypan, and cymling) are all the samespecies, Cucurbita pepo, andthat winter squash (butternut,acorn, hubbard, butterball,spaghetti, pumpkin) are also all the same species, Cucurbitamaxima. Ask students to writean explanation of how peoplehave achieved such a variety ofsquash.

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Cultural DiversityCultural Taboos AgainstInbreedingAlthough inbreeding can result in high ratesof stillbirths and children with congenitaldisorders, scientists are not sure whethertaboos against incest are culturally or natu-rally selected. Explain to students thattaboos against inbreeding are not universal,

indicating that their origins are culturalrather than genetic. However, individualsbrought up in close proximity to each otheras family members usually are less likely todevelop a sexual interest in each other. Thissuggests that incest taboos may have a bio-logical component.

When is a test cross practical? How can you tell the geno-type of an organism that has a dominant phenotype? Thereare two ways. The first is through the use of pedigree studies.This technique works well as long as a family is fairly largeand records are accurate. The second technique is a test cross.Test crosses help determine whether an organism is homozy-gous or heterozygous for a dominant trait.

AnalysisYour pet guinea pig

has black hair. This trait is dominant and can be represented by a B allele. Your neighbor has a white guinea pig. This trait is recessive and can be repre-sented by a b allele. You want to breed the two guinea pigs but want all offspring from the mating to be black. You are not sure, how-ever, of the genotype of your black guinea pig and want tofind out before starting the breeding program.

Thinking Critically1. What may be the possible genotypes of your black guinea

pig? Explain why you are unable to tell even though theanimal has a black phenotype.

2. What is the genotype of the white guinea pig? Explainhow you are able to tell.

3. Outline a procedure that will determine the coat colorgenotype for your black guinea pig. Include Punnettsquares to illustrate the conclusions that you will reach.(Hint: You will be doing a test cross.)

4. What options do you have for breeding all black offspringif you determine that your guinea pig is heterozygous forblack color?

5. Explain why a test cross is not practical when trying todetermine human genotypes.

Problem-Solving Lab 13-1Problem-Solving Lab 13-1 Designing anExperiment

Determining Genotypes A good breeder must be careful to

determine which plants or animalswill have the greatest chances oftransmitting a desired trait to thenext generation. Choosing the bestparents may be difficult. The geno-type of an organism that is homozy-gous recessive for a trait is obvious toan observer because the recessivetrait is expressed. However, organ-isms that are either homozygousdominant or heterozygous for a traitcontrolled by Mendelian inheritancehave the same phenotype. How can abreeder learn which genotype shouldbe used for breeding?

Test crosses can determine genotypes

One way to determine the geno-type of an organism is to perform atest cross. A test cross is a cross ofan individual of unknown genotypewith an individual of known geno-type. The pattern of observed pheno-types in the offspring can help deter-mine the unknown genotype of theparent. Usually, the parent with theknown genotype is homozygousrecessive for the trait in question.

Many traits, such as disease vulner-ability in rose plants and progressiveblindness in German shepherd dogs,are inherited as recessive alleles.These undesired traits are maintainedin the population by carriers of the trait. A carrier, or heterozygousindividual, appears to have the samephenotype as an individual that ishomozygous dominant.

What are the possible results of atest cross? If the known parent ishomozygous recessive and theunknown parent is homozygous dom-inant, all of the offspring will be het-erozygous for the trait and will showthe dominant trait (be phenotypically

dominant), as shown in Figure 13.3on the next page. However, if theorganism being tested is heterozy-gous, the predicted 1: 1 phenotypicratio will be observed. If any of theoffspring have the undesired trait, theparent in question must be heterozy-gous. Doing the Problem-Solving Labwill show you how to set up and ana-lyze a test cross.

13.1 APPLIED GENETICS 347

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Purpose Students will describe a proce-dure for determining a genotype.

Process Skillsthink critically, apply concepts,draw a conclusion

Teaching Strategies■ Pedigree studies will work indetermining genotypes onlywhen there are many offspringand when certain individuals arehomozygous recessive. Illustratethis point with a pedigree thatshows a small family of two par-ents (both with a dominant phe-notype) and one offspring (with adominant phenotype). There isno way to predict whether anyindividuals are heterozygous.

Thinking Critically

1. BB or Bb; both genotypesshow a black phenotype.

2. bb; the trait is recessive andthe white phenotype canshow only when both allelesare recessive.

3. Mate an unknown blackguinea pig with a whiteguinea pig. If all offspring areblack, you may conclude thatthe black guinea pig is BB. Ifany white offspring are born,however, the black guinea pigmust be heterozygous.

4. Continue to breed yourguinea pig with a whiteguinea pig but understandthat half of all offspring willbe white, or do not breedyour guinea pig, or breedyour black guinea pig with ahomozygous black guineapig. In the last case, all off-spring will be black but halfwill be heterozygous.

5. Because humans usually haveonly one offspring per birth,it would require too muchtime for determining geno-type. The person would haveto mate with a homozygousrecessive individual for thetrait in question.

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Problem-Solving Lab 13-1Problem-Solving Lab 13-1Inbreeding develops pure lines To make sure that breeds consis-

tently exhibit a trait and to eliminateany undesired traits from their breed-ing lines, breeders often use themethod of inbreeding. Inbreeding ismating between closely related indi-viduals. It ensures that the offspringare homozygous for most traits.However, inbreeding also brings outharmful, recessive traits because thereis a greater chance that two closelyrelated individuals may both carry aharmful recessive allele for the trait.

Horses and dogs are two examplesof animals that breeders have devel-oped as pure breeds. A breed (called acultivar in plants) is a selected groupof organisms within a species that hasbeen bred for particular characteris-tics. For example, the pure breedGerman shepherd dog has long hair,is black with a buff-colored base, hasa black muzzle, and resembles a wolf,Figure 13.1.

Hybrids are usually bigger and better

Selective breeding of plants canincrease productivity of food forhumans. For example, plants that aredisease resistant can be crossed withothers that produce larger and morenumerous fruit. The result is a plantthat will produce a lot of fruit and bemore disease resistant. Recall that ahybrid is the offspring of parents thathave different forms of a trait. Whentwo cultivars or closely relatedspecies are crossed, their offspringwill be hybrids. Hybrids produced bycrossing two purebred plants areoften larger and stronger than theirparents. Many crop plants such aswheat, corn, and rice, and gardenflowers such as roses and dahlias havebeen developed by hybridization.Figure 13.2 shows some examples.

One example of the effectiveness ofselective breeding is seen in a com-parison of milk production in cattle in1947 and 1997. In 1947, an averagemilk cow produced 4997 pounds ofmilk per year. In 1997, 50 years later,an average milk cow produced 16 915pounds of milk in a year, more thanthree times more milk per cow. Fewerthan half the number of cows are nowneeded to produce the same amountof milk, resulting in savings for dairyfarmers.

Figure 13.1A pure breed, such as this German shep-herd dog, is homozy-gous for the particu-lar characteristics forwhich it has beenbred.

Figure 13.2 These roses, all dif-ferent cultivars, havebeen hybridized tocombine traits suchas color, aroma, andflower shape.

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Knowledge Have studentswrite a paragraph differentiatingamong selective breeding, inbreed-ing, and hybridization. What arethe goals of each? Selective breedingattempts to gradually increase thefrequency of desirable alleles in a pop-ulation by selecting certain individu-als as parents. Inbreeding ensuresthat a breed is homozygous fordesired traits. Hybridization com-bines two desirable traits of differentbreeds into a single organism by mat-ing the breeds. L2

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AssessmentAssessment

Quick DemoQuick Demo

Have volunteers bring in pic-tures of their pets and pets’parents, offspring, and/or sib-lings. At least some of the ani-mals should be mixed breeds.Arrange the pictures on posterboard and have studentsattempt to match the animalswith their relatives. Discuss thecharacteristics used to identifythe pet families.P

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BIOLOGY JOURNAL BIOLOGY JOURNAL

Test CrossesLinguistic Ask students to write a para-graph that tells why it would not be

helpful when conducting a test cross to matethe animal being tested with either homozy-gous dominant or heterozygous individuals.Have students use Punnett squares to helpwith technical explanations. Mating with a

homozygous dominant individual would notdetermine the genotype of the animal beingtested because all offspring would show thedominant trait. If the animal being testedwere heterozygous, mating with a heterozy-gous test animal reduces the chances of anoffspring showing the recessive trait from 50% to 25%.

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VIDEODISCThe Secret of LifeTest Cross-Homozygous

Test Cross-Heterozygous

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Skill Ask students to prepare Punnettsquares that would illustrate the results of a cross between two heterozygous blackguinea pigs and between one heterozygousand one homozygous black. Which mating would be preferred if only black offspring were desired? Use the Performance TaskAssessment List for Scientific Drawing inPASC, p. 55. L1

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Resource ManagerResource ManagerReinforcement and Study Guide, p. 55

Laboratory Manual, pp. 91-94 L2

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Figure 13.3 In this test cross ofAlaskan malamutes,the known test dog ishomozygous recessivefor a dwarf allele (dd),and the other dog’sgenotype is unknown.

Section AssessmentSection Assessment

Understanding Main Ideas1. A test cross made on a cat that may be heterozy-

gous for a recessive trait produces ten kittens,none of which has the trait. What is the pre-sumed genotype of the cat? Explain.

2. Suppose you want to produce a plant cultivarthat has red flowers and speckled leaves. Youhave two cultivars, each having one of thedesired traits. How would you proceed?

3. Why is inbreeding rarely a problem among ani-mals in the wild?

4. Hybrid corn is produced that is resistant to bacter-ial infection and is highly productive. What mighthave been the phenotypes of the two parents ?

Thinking Critically5. What effect might selective breeding of plants

and animals have on the size of Earth’s humanpopulation? Why?

6. Making and Using Tables A bull is suspectedof carrying a rare, recessive allele. Following atest cross with a homozygous recessive cow, fourcalves are born, two that express the recessivetrait and two that do not. Draw a Punnett squarethat shows the test cross, and determine thegenotype of the bull. For more help, refer toOrganizing Information in the Skill Handbook.

SKILL REVIEWSKILL REVIEW

The unknown dog canbe either homozygousdominant (DD) or het-erozygous (Dd) forthe trait.

AA

If the unknowndog’s genotypeis homozygousdominant, all ofthe offspring willbe phenotypi-cally dominant.

BBDD

d

Dd Dd

Dd

D

dd

d

D

Offspring: all dominant

Homozygous Homozygous

Dd

Dd

d

Dd Dd

dd

D

dd

d

d

Offspring: 1/2 dominant1/2 recessive

Heterozygous Homozygous

dd

If the unknowndog’s genotype isheterozygous, halfthe offspring willexpress the reces-sive trait andappear dwarf. Theother half willexpress the domi-nant trait and be ofnormal size.

CC

Dd Dd Dd

dd

dd

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3 AssessCheck for UnderstandingHave students explain the role ofa test cross and what breedingprograms attempt to accomplish.

ReteachAlbinism, or white fur, in rabbitsis due to a recessive allele. Let A= normal fur pigment and a =albinism (no fur pigment). Abreeder wishes to know if a malerabbit is homozygous or het-erozygous for pigmented fur.Have students diagram the possi-ble crosses in Punnett squaresand interpret the results.

ExtensionHave students explore the prob-lems that occur when horses arebred to donkeys to producemules and hinnies. Have themspeculate as to how Mendel’s lawsmight have differed if he hadworked with these animals.

Knowledge Provide stu-dents with a test cross for a trait.Ask students to complete thegenotypes for the test cross.

4 CloseDiscussionDiscuss with students that there iscurrently an interest in eggs withlow cholesterol content. Then askstudents how they might proceedto breed chickens that producesuch low-cholesterol eggs.

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Section AssessmentSection AssessmentSection Assessment1. The cat is probably homozygous domi-

nant. If it were heterozygous, therewould probably have been some off-spring with the recessive trait.

2. First breed the red flower plants amongthemselves to ensure that they are breed-ing true. Do the same for the plants with

speckled leaves. Then, hybridize the twocultivars by breeding them together.

3. In nature, mate selection is random andthe chance that a mate will be closelyrelated is greatly reduced.

4. One parent was highly productive. Theother was resistant to bacterial infection.

5. Selective breeding can increase crop sizeand provide for more nutritious and

more disease-resistant crops, and thismight increase the human population.

6. Students’ Punnett squares should showa cross between a homozygous reces-sive individual and a heterozygousindividual. Half the offspring will benormal and half will express the reces-sive trait. This is what was observed, sothe bull was heterozygous.348

Section

13.2 RECOMBINANT DNA TECHNOLOGY 349

Genetic EngineeringYou learned that selective breeding

is a form of genetic technologybecause it increases the frequency ofan allele in a population. You alsolearned that it may take many gener-ations of breeding for a trait tobecome homozygous and consis-tently expressed in the population.Genetic engineering is a muchfaster and more reliable method forincreasing the frequency of a specificallele in a population. This methodinvolves cutting—or cleaving—DNAfrom one organism into small frag-ments and inserting the fragmentsinto a host organism of the same or adifferent species. You may also heargenetic engineering referred to as

recombinant (ree KAHM buh nunt)DNA technology. RecombinantDNA is made by connecting, orrecombining, fragments of DNAfrom different sources.

Transgenic organisms containrecombinant DNA

Recombinant DNA can be insertedinto a host organism’s chromosomesand that organism will use the foreignDNA as if it were its own. Plants andanimals that contain functionalrecombinant DNA, such as the glow-ing tobacco plant, are known astransgenic organisms because theycontain foreign DNA.

The glowing tobacco plant is theresult of a three-step process that isused to produce a transgenic organism.

You have learned that DNA canfunction like a zipper, opening up toallow replication and transcription.

Scientists have found a series of enzymesthat can cut DNA at specific locations,sometimes unzipping the strands as theycut. These enzymes allow scientists to insertgenes from other sources intoDNA. The glowing plantshown here was created byinserting a firefly geneinto the DNA of atobacco plant.

SECTION PREVIEW

ObjectivesSummarize the stepsused to engineer trans-genic organisms.Give examples ofapplications and bene-fits of genetic engineer-ing.

Vocabulary genetic engineeringrecombinant DNAtransgenic organismrestriction enzymevectorplasmidgene splicingclone

13.2 Recombinant DNATechnology

OriginWORDWORD

transgenicFrom the Latinword trans, meaning“across,” and theGreek word genos,meaning “race.” Atransgenic organismcontains genes fromanother species.

Transgenic tobacco plant(above) and firefly (inset)

349

Section 13.2

PrepareKey ConceptsStudents will learn that geneticengineering involves a three-stepprocess that produces a transgenicorganism. Students will exploretechniques used to sequence DNAand applications of DNA technol-ogy in agriculture, industry, andmedicine.

Planning■ Make cutouts of bases for the

Meeting Individual Needs.


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Describe the new food. Why is it better?

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Matching Restriction Enzymes toCleavage Sites Many restrictionenzymes cut sequences of DNA thatare palindromes. As a result of cuts tothe DNA, single-stranded sequences ofDNA are left dangling at the ends of afragment. These ends are available forpairing with their complementary basesin a plasmid or piece of viral DNA.

Procedure! Copy the data table below.

@ Figure out which restriction enzyme will cleave each DNAfragment. Use the following guides.Enzyme D cleaves at an A-A site and leaves 3 single-

stranded bases on each end. Enzyme E cleaves at a G-G site and leaves 4 single-

stranded bases on each end. Enzyme F cleaves at a G-A site and leaves 4 single-

stranded bases on each end. # Draw in the action of each enzyme. Record its letter.$ Diagram each fragment of DNA as it would appear if

cleaved by the proper restriction enzyme. % Use the top row in the table as an example and guide.

Analysis1. Use the example provided in the data table to illustrate a

single-stranded dangling end of DNA.2. Record the DNA base sequence that must be present on a

piece of viral DNA if these ends could “stick to” the dan-gling bases in the example shown in the data table.

3. Are restriction enzymes very specific as to where theycleave DNA? Explain your answer and give an example.

MiniLab 13-1MiniLab 13-1Vectors transfer DNA

Loose fragments of DNA do notreadily become part of a host organ-ism’s chromosomes. To make thisprocess easier, the fragments are firstattached to a vehicle that will carrythem into the host organism’s cells.In the case of the transgenic tobaccoplant, the light-producing fireflyDNA has to be inserted into bacterialDNA before it can be placed insidethe plant. The bacterial DNA is avector. A vector is a means by whichDNA from another species can becarried into the host cell. Vectorsmay be biological or mechanical.

Biological vectors include virusesand plasmids. A plasmid, shown inFigure 13.5, is a small ring of DNAfound in a bacterial cell. The genes itcarries are different from those onthe larger bacterial chromosome.

Two mechanical vectors carry for-eign DNA into the nucleus of a cell.One, a micropipette, is inserted into acell; the other is a tiny metal bulletcoated with DNA that is shot into thecell using a device called a gene gun.


T

A

GGC C T A

GG T C C

DNA fragment

DNAfragment

Cleavedfragmentof DNA

Action ofrestrictionenzyme

Enzymeletter(D-F)

GGTACC

CCATGG

GGTACC

CCATGG

G GTACC

CCATG G

E

CCATGG

GGTACC

CAAT TG

GTTAAC

GATATC

C TATAG

Data Table

Figure 13.5 Plasmids are small rings of DNA. The largering is the bacterium’s chromosome.

Applying Concepts

Magnification: 157 500�

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Purpose Students will match restrictionenzymes with their proper basesequences in a DNA strand.

Process Skillsthink critically, analyze informa-tion, apply concepts, define oper-ationally, draw a conclusion

Teaching Strategies■ Be sure that students have readover the applicable material inthe text before starting thisMiniLab.■ Allow students to work insmall groups to complete thisactivity.■ Remind students that theDNA segments shown are only asmall portion of the DNA mole-cule.■ Point out to students that inthe example provided, the com-plementary bases are joinedtogether to form a double strandbut are not joined together afterbeing cleaved by the enzyme.Thus, single-stranded sticky endsare created.

Expected ResultsSee data table below.

Analysis1. GTAC– is a dangling end.2. –CATG3. Yes; each enzyme can cleave

only a specific site and canleave only a specific numberof single-stranded DNAbases. Enzyme F cleavesbetween G and A but mustleave 4 bases in the danglingend.

Portfolio Ask students toinvent a plasmid strand of DNAthat would fit the cleaved ends ofthe second example in the datatable. Use the Performance TaskAssessment List for Invention inPASC, p. 45. L2

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MiniLab 13-1MiniLab 13-1restriction enzymes are bacterialproteins that have the ability to cutboth strands of the DNA molecule ata specific nucleotide sequence. Thereare hundreds of restriction enzymes,each capable of cutting DNA at aspecific point in a specific nucleotidesequence. The resulting DNA frag-ments are of different lengths. Whenrestriction enzymes cut DNA, it issimilar to cutting a zipper into piecesby cutting only between certain teethof the zipper. Note in Figure 13.4that the same sequence of bases isfound on both DNA strands, butrunning in opposite directions. Thisarrangement is called a palindrome(pal uhn drohm). Palindromes arewords or sentences that read thesame forwards or backwards. Thewords mom and dad are two very sim-ple examples of palindromes.

Some enzymes produce fragmentsin which the DNA is cut straightacross both strands. These are calledblunt ends. Other enzymes, such asthe enzyme called EcoR1, cut palen-dromic sequences of DNA by unzip-ping them for a few nucleotides, asshown in Figure 13.4. When thisDNA is cut, double-stranded frag-ments with single-stranded ends areformed. The single-stranded endshave a tendency to join with other sin-gle-stranded ends to become doublestranded, so they attract DNA theycan join with. For this reason, theseends are called sticky ends. This is thekey to recombinant DNA because ifthe same enzyme is used to cleaveDNA from two organisms, such asfirefly DNA and bacterial DNA, thetwo pieces of DNA will have match-ing sticky ends and will join togetherat these ends. When the firefly DNAjoins with bacterial DNA, recombi-nant DNA is formed. The MiniLabon the opposite page models the wayrestriction enzymes work.


Figure 13.4In the presence of the restrictionenzyme EcoR1, a double strand of DNA containing thesequence—GAATTC—is cleaved betweenthe G and the A.

The first step is to isolate the foreignDNA fragment that will be inserted.The second step is to attach theDNA fragment to a “vehicle.” Thethird step is the transfer of the vehi-cle into the host organism. Each ofthese three steps now will be dis-cussed in greater detail.

Restriction enzymes cleave DNATo isolate a DNA fragment, small

pieces of DNA must be cut from alarger chromosome. In the exampleof the glowing tobacco plant, thisfragment is a section of firefly DNAthat codes for the light-producingenzyme. The discovery in the early1970s of DNA-cleaving enzymesmade it possible to cut DNA. These

G

A T TG A C

A T TA CG

A

TT

G

A

C

ATT GAC

ATT AC

A

TT

G

A

C

G

A T TG A C

ATT GAC

A T TA C

ATT GAC

Cleavage

Cut

Splicing

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2 TeachDiscussionAsk students what geneticchanges people might want toengineer into their pets. Studentsmight suggest stamina, intelligence,hair retention, and disease resistance.

Concept DevelopmentTo help students rememberEcoR1, explain that this enzymewas discovered in the bacteriumEscherichia coli. E comes fromEscherichia, co from coli, R fromRestriction enzyme, and 1 indi-cates that this enzyme was thefirst restriction enzyme found inthis bacterium.


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Visually ImpairedKinesthetic Have students who arevisually impaired use large pieces of

cardboard cut into four shapes (severalpieces of each shape) to represent each ofthe four bases: A, T, C, and G. Use them todemonstrate a palindrome and to modelthe action of restriction enzymes.P

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DNAfragment

Cleavedfragmentof DNA

Action ofrestrictionenzyme

Enzymeletter(D-F)

GGTACC

CCATGG

GGTACC

CCATGG

G GTACC

CCATG G

E

E

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F

CCATGG

GGTACC

CAAT TG

GTTAAC

GATATC

C TATAG

Data Table

CCATGG

GGTACC

CAATTG

GTTAAC

GATATC

CTATAG

CCATG G

G GTACC

CA ATTG

GTTA AC

G ATATC

CTATA G

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Cloning of animals So far, you have read about cloning

a single gene. For decades, scientistsattempted to expand the techniquefrom a single gene to an entireorganism. The most famous clonedanimal is Dolly, the sheep. You canread more about Dolly in theBioTechnology feature at the end ofthis chapter. Although their tech-niques differ, scientists are comingcloser to perfecting the technique ofcloning animals. One of the benefitsfor humans in cloning animals is thatranchers and dairy farmers can cloneparticularly productive, healthy ani-mals to increase yields.

Sequencing DNA Genetic engineering techniques

can also provide pure DNA for use ingenetic studies. After large amountsof DNA have been produced bycloning, scientists can determine thesequence of DNA bases. This infor-mation is critical for scientists becausethey can identify and study specificgenes and pieces of DNA that regu-late the transcription of these genes.

In DNA sequencing, millions ofcopies of a double-stranded DNAfragment are cloned by bacterial cul-ture of plasmids. Then, the strandsare separated from each other. Thesingle-stranded fragments are mixedin test tubes with enzymes, radioac-tively labeled nucleotides, and dyes toproduce many new complementarystrands of varying lengths. Thesenew strands can be separated accord-ing to size by gel electrophoresis (ihlek troh fuh REE sus), producing apattern of dyed bands in the gel. Theradioactive label allows a direct read-ing of the sequence of bases on x-rayfilm. How do the DNA strands sepa-rate from each other in the gel? Readthe Inside Story on the next page tofind out.

Applications of DNA Technology

Once it became possible to transfergenes from one organism to another,large quantities of hormones andother products could be produced.How is this technology of use tohumans? Many species of bacteriahave been engineered to producechemical compounds that are of useto humans. The three main areas pro-posed for recombinant bacteria are inindustry, medicine, and agriculture.

Recombinant bacteria in industryIn industry, recombinant bacteria

have been engineered to break downpollutants into harmless products.Laboratory experiments with recom-binant bacteria first showed that theseengineered bacteria could degrade oilmore rapidly than the same species ofnaturally occurring bacteria, as seenin Figure 13.7. These recombinantbacteria were used with some successin the Gulf of Mexico to clean up anoil spill off the coast of Texas. Miningcompanies also are interested in bio-engineering bacteria that will extractvaluable minerals from ores.

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Figure 13.7 The first patentedorganism, a bac-terium that breaksdown oil, was engi-neered by Dr. AnandaChakrabarty. Theflask in the rear con-tains oil and naturalbacteria. The flask atthe front contains theengineered bacteriaand is almost free of oil.

353

EnrichmentIntroducing human genes intoplants that are grown in the fieldhas obvious benefits in producinglarge amounts of proteins. Criticspoint out that the environmentaland ethical implications of theseexperiments have not beenexplored. To invite a class discus-sion on this topic, ask students thefollowing question: What mightbe the consequences on the envi-ronment if the new genes get intothe wild gene pool?

Performance Assessmentin the Biology Classroom, p.19,Making a Model of RecombinantDNA. Have students carry outthis activity after they have com-pleted the study of recombinantDNA. L1

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Foreign DNA(gene for human growth hormone)

Recombinedplasmid

Recombinant DNA

Reproduction

Cloned cells with recombinant DNA

Humangrowth

hormone

Cleavage sites

Plasmid

E. coli

Bacterialchromosome

Bacterialplasmids

Gene splicingAs you have learned, if a plasmid

and foreign DNA have been cleavedwith the same restriction enzyme, theends of each will match and they willjoin together, reconnecting the plas-mid ring. Rejoining of DNA frag-ments is called gene splicing. Theforeign DNA is recombined into aplasmid or viral DNA with the helpof a second enzyme. You can practicemodeling gene splicing in the BioLabat the end of this chapter.

Gene cloningAfter the foreign DNA has been

spliced into the plasmid or the virusvector, the recombined DNA istransferred into a cell of the hostorganism. The host cell can be aplant or animal cell or a bacterial cell.When the host cell prepares todivide, it copies the recombinantDNA along with its own DNA. Theprocess of making extra copies ofrecombinant DNA is a form ofcloning. Clones are genetically iden-tical copies. Each identical recombi-nant DNA molecule is called a geneclone. Gene cloning is an important

step in the process of genetic engi-neering because multiple copies ofthe desired DNA are produced.

Why clones are possibleCloning is possible because a for-

eign piece of DNA introduced into ahost cell has been integrated into thatcell so completely that the foreignDNA is replicated as if it were thehost’s DNA. Each cell makes thedesired product. For example, if theforeign DNA contains a gene forinsulin production, each cell contain-ing that DNA will make insulin.

An advantage to using bacterialcells to clone DNA is that theyreproduce quickly. If a bacterial cellwere engineered to produce humangrowth hormone, billions of clonedcells could generate the large quanti-ties of hormone that are needed forpatients who require it. It would beimpossible to obtain such largeamounts of the product from humansbecause hormones are produced inthe body in very small amounts.Figure 13.6 summarizes the forma-tion and cloning of recombinantDNA in a bacterial host cell.


Figure 13.6Foreign DNA isspliced into a plasmidvector. The recom-bined plasmid thencarries the foreignDNA into the bacter-ial cell, where it iscloned when the cellreproduces. If the for-eign DNA containeda gene for humangrowth hormone,each cell will makethe hormone.

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EnrichmentIntrapersonal Mice withmutant genes are particu-

larly valuable to scientists study-ing human diseases. Using agrant from the National Instituteof General Medical Services, sci-entists have developed what theycall knockout mice. Have capablestudents find out how these miceare produced and how scientistsstudy the effect of missing genesin the mice on conditions such asaging or cancer. L3

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P R O J E C TEnzyme Model

Kinesthetic Have students build amodel demonstrating the use of

restriction enzymes on DNA. They coulduse various materials to represent theDNA nucleotides, such as colored pushpins, colored paper clips, or M & Ms.P

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Internet Address Book

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the space below for quick reference.

The BioLab at theend of the chaptercan be used at thispoint in the lesson.

INVESTIGATEINVESTIGATE

CD-ROMBiology: The Dynamicsof Life

Animation: Gene CloningDisc 2

VIDEODISCBiology: The Dynamicsof Life

Gene Cloning (Ch. 38)Disc 1, Side 1, 23 sec.

The Infinite Voyage Miracles byDesign, Biodegradable Plastic:The Miracle Material? (Ch. 4)7 min.

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!7KVF"The Infinite Voyage The Geo-metry of Life, ManipulatingGenetic Engineering (Ch. 10)3 min.

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Engineered BacteriaLinguistic Have students researchand write an essay on whether sci-

entists should be allowed to alter bacte-ria genetically and release them into theenvironment. Have students include acopy of their essays in their portfolios.P

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Bioengineering (Ch. 37)Disc 1, Side 1, 57 sec.

Recombinant DNA (Ch. 36)Disc 1, Side 1, 38 sec.


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How might gene transfer be verified? When you sprayweeds with a chemical herbicide, they die. Glyphosate is the active ingredient in some herbicides. The problem withherbicides, however, is that glyphosate often gets sprayedaccidentally onto crops and they also die. A certain gene will confer resistance to glyphosate. If this gene can begenetically engineered into crop plants, they will survivewhen sprayed with this herbicide. The following experimentis a test to determine to which plants the gene has been successfully transferred.

AnalysisTwo groups of pots are each planted with three plants,

according to the diagram above. Plants A, B, and C aresprayed with water. Plants D, E, and F are sprayed with a her-bicide containing glyphosate.

Thinking Critically1. Assume that the transfer of glyphosate resistance was suc-

cessful in plant F. Predict whether each of plants D, E, andF will remain healthy after being sprayed with glyphosate.Explain your prediction.

2. Predict whether plant F will remain healthy if the transferof glyphosate resistance was not successful.

3. Which plants are transgenic organisms? Explain youranswer.

4. Explain why a glyphosate-resistant plant will produceseeds that show resistance to the herbicide.

5. Why were plants A, B, and C sprayed with water? Whatwas the purpose of these plants in the experiment?

Problem-Solving Lab 13-2Problem-Solving Lab 13-2 Thinking CriticallyRecombinant bacteria in medicine

In medicine, pharmaceutical com-panies already are producing mole-cules made by recombinant bacteriato treat human diseases. Recombinantbacteria are employed in the produc-tion of human growth hormone totreat dwarfism, and of insulin to treatdiabetes. The human gene for insulinis inserted into a bacterial plasmid bygenetic engineering techniques.Recombinant bacteria produce suchlarge quantities of insulin that theybulge. Another strain of recombinantbacteria is being used to producephenylalanine, an amino acid that isneeded to make aspartame, an artifi-cial sweetener found in many dietproducts.

Transgenic animals Transgenic animals are opening up

new avenues through which scientistscan study diseases and the role specificgenes play in an organism. A favoriteanimal for transgenic studies is themouse because mice reproducequickly, within three weeks, andmouse chromosomes are similar tohuman chromosomes. In addition, sci-entists know a lot about where genesare located on mouse chromosomes.The roundworm Caenorhabditis elegansis another organism with simplegenetics that is well understood and isused for transgenic studies. A thirdanimal commonly used for transgenicstudies is the fruit fly, Drosophilamelanogaster.

Although animals such as a wormand a fruit fly may seem very differentfrom humans, it is surprising howmany genes are common to all. Oneway in which scientists use geneticengineering is to create animals withhuman diseases. By studying theseanimals, scientists hope to treat andcure these diseases in humans.


Sprayed with water

Sprayed with herbicide

No resistanceto herbicide

Resistanceto herbicide

Received genefor resistance

A B C

D E F

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Purpose Students will analyze the resultsof an experiment designed toillustrate genetic transfer.

Process Skillsthink critically, analyze informa-tion, apply concepts, draw a con-clusion, interpret data, predict

BackgroundGlyphosate blocks the synthesisof amino acids phenylalanine,tyrosine, and tryptophan. Cellsunable to form these amino acidsdie. Glyphosate inhibits the en-zyme EPSP synthase from syn-thesizing these amino acids.

Teaching Strategies■ You may wish to discuss thetechnique that is used to transferthe resistant gene to its hostplant. The organism or vector isAgrobacterium tumefaciens, a bac-terium that infects plants.■ Make sure that studentsunderstand that plants sprayedwith glyphosate will die if they donot contain genes making themresistant to the chemical.■ Students may work in smallcooperative groups to completethis activity.

Thinking Critically

1. Plants E and F will remainhealthy because they have thegene that imparts resistance.Plant D will die because it isnot resistant to glyphosate.

2. If resistance is not trans-ferred, plant F will diebecause it is not resistant toglyphosate.

3. Plants C and F are transgenicorganisms. They contain for-eign DNA.

4. All the cells of a resistantplant, including cells thatproduce gametes, contain thegene for resistance.

5. Plants A, B, and C were con-trols. They were sprayed withwater to show that sprayingdoes not transfer resistance tothe chemical.

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DNA fragments

Completed gel

Longer fragments

Shorter fragments

Negative end

Powersource

Positive end


Gel Electrophoresis

Restriction enzymes are the perfect tools for cuttingDNA. However, once the DNA is cut, a scientist needs

to determine exactly what fragments have been formed.Once DNA fragments have been separated on a gel, manyother techniques, such as DNA sequencing, can be used tospecifically identify a DNA fragment.

Critical Thinking Why might gel electrophoresis be animportant step before DNA sequencing can be done?

Before the DNA fragments are added to the wells, they are treated with a dye

that glows under ultraviolet light, allowing the bands to be studied.

INSIDESSTORTORYY

INSIDE

Restriction enzymes Either oneor several restriction enzymes isadded to a sample of DNA. Theenzymes cut the DNA into fragments.

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The electrical field The gel is placed ina solution, and an electrical field is set upso that one end of the gel is positive andthe other end is negative.

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The gel A gel,with a consistencysimilar to gelatin,is formed so thatsmall wells are left at one end.Into these wells,small amounts ofthe DNA sampleare placed.

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The fragments move The negativelycharged DNA fragments travel toward the pos-itive end. The smaller the fragment, the fasterit moves through the gel. Fragments that arethe farthest from the well are the smallest.

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Gel

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IINSIDENSIDESSTORTORYY

INSIDE

Purpose Students will learn how gel elec-trophoresis separates DNA frag-ments of different sizes.

BackgroundGel electrophoresis is a basictechnique used in the preparationof DNA samples for other tech-niques such as DNA sequencing.

Teaching Strategies■ Give students several paper“DNA fragments” of differentsizes. Have them draw what a gelelectrophoresis of these frag-ments would look like. Make surethey indicate at which end of thegel the fragments were added.

■ Have students describe orallythe steps necessary to run a gel.

Visual Learning■ Use colored chalk to demon-

strate different sized DNAfragments that have been runin a gel.

Critical ThinkingDNA sequencing can be doneonly on small pieces of DNA. Gelelectrophoresis separates the smallpieces of DNA from large piecesbefore sequencing takes place.

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Reinforcement and StudyGuide, pp. 56-57

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VIDEODISCThe Secret of LifeElectrophoresis and PCR Segment

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Performance Have students designand carry out an experiment to test whetherglyphosate (Roundup) affects seeds of plants.Use the Performance Task Assessment Listfor Designing an Experiment in PASC, p. 23.L3

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Recombinant bacteria in agriculture

One species of bacteria has alreadybeen engineered successfully for useon agricultural crops. These particularbacteria normally occur on strawberryplants and cause frost damage to theleaves and fruits because ice crystalsform around a protein on the surfaceof each bacterium. After engineeringthe bacteria to remove the gene forthis protein, the recombinant bacteriaare applied to the leaves of the plants.They replace the natural bacteria, andfrost damage is prevented.

Farmers hope that another speciesof bacteria that lives in soil and in theroots of some plants can be engineeredto increase the rate of conversion of

atmospheric nitrogen to nitrates, anatural fertilizer used by plants. Ifthis can be accomplished, farmerswill be able to save money by cuttingback on fertilizer.

Transgenic plantsThe Problem-Solving Lab on the pre-

vious page shows one way plants couldbe improved by genetic bioengineer-ing. Plants are more difficult to genet-ically engineer than bacteria becauseplant cells do not have the plasmids orkinds of viruses needed for taking upforeign pieces of DNA that bacterialcells have. Also, because plant cellsare surrounded by thick cell walls, itis difficult to insert the foreign DNA.

A bacterium that normally causestumorlike growths in the tissues ofcertain plants, Figure 13.8, has beenused to carry foreign genes into plantcells. Most engineering of plants usesmechanical vectors such as DNA-coated “bullets.” Brief jolts of high-voltage electricity also can be used.The jolts cause temporary pores toform in the plasma membrane,through which the DNA can enter.

Plants have been genetically engi-neered to resist herbicides, produceinternal pesticides, or increase theirprotein production. These plantshave been used in field trials, and arenow used extensively.


Understanding Main Ideas1. How are transgenic organisms different from

natural organisms of the same species?2. How are sticky ends important in making

recombinant DNA?3. Why is it presently more difficult to engineer

transgenic plants and animals than it is to engineer bacteria?

4. Explain two ways in which recombinant bacteriaare used for human applications.

Thinking Critically5. Many scientists consider genetic engineering to

be simply an efficient method of selective breed-ing. Explain.

6. Sequencing Order the steps in producingrecombinant DNA in a bacterial plasmid. Formore help, refer to Organizing Information inthe Skill Handbook.


Figure 13.8 The bacterium thatcauses these tumor-like plant galls is theonly known biologi-cal plant vector.Unfortunately, itdoes not work onmany kinds of plants.


3 AssessCheck for UnderstandingWrite a sequence of DNA thatincludes two of the sequencesGAATTC and ask students todemonstrate where EcoR1 willcut the strand of DNA.

ReteachKinesthetic Have studentsmodel how restriction

enzymes create sticky ends, usingother restriction enzymes so theycan see that choice of the particu-lar enzyme is important. Forexample, BamH1 recognizesGGATCC and cuts between thetwo Gs. Hind III recognizesAAGCTT and cuts between thetwo As.

ExtensionInterested students can look intothe applications of protein engi-neering and computer modelingto produce modified natural pro-teins or to create entirely newproteins.

Knowledge Have studentssummarize the formation ofrecombinant DNA.

4 CloseDiscussionLead into the next section by dis-cussing how DNA technologymay provide therapy for manygenetic disorders.

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Section AssessmentSection AssessmentSection Assessment1. Transgenic organisms contain DNA

from other sources.2. Sticky ends allow the cleaved DNA to

join to complementary single strands onDNA molecules from another organism.

3. Plants and animals do not readily acceptplasmids into their DNA, and plants

have tough cell walls that make it diffi-cult to insert DNA.

4. Recombinant bacteria produce humangrowth hormone, insulin, and phenyl-alanine. They are also used for bettercrop production such as frost-resistantstrawberries.

5. Answers may include that both genetic

engineering and selective breedinginvolve increasing the frequency of adesired gene in a population by humanintervention

6. Cleave the plasmid and foreign DNAwith the same restriction enzyme, andthe sticky ends will join, reconnectingthe plasmid ring.

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Section

13.3 THE HUMAN GENOME 357

Mapping andSequencing the HumanGenome

In 1990, scientists in the UnitedStates organized the Human GenomeProject. It is an international effortto completely map and sequence thehuman genome, the approximately80 000 genes on the 46 human chromosomes. The project is stillunderway. Maps currently are beingprepared that show the locations ofknown genes on each chromosome.At the same time, the sequence ofthe 3 billion base pairs of DNA inthe human genome is being analyzed

and mapped. Eventually, the twomaps will be synchronized. TheMiniLab on the next page gives youan idea of the size of the humangenome.

Linkage mapsThe locations of only a few thou-

sand of the total number of knownhuman genes have been mapped onparticular chromosomes. This meansthat for most human genes, scientistsdon’t know the exact or even theapproximate locations on chromo-somes. The genetic map that showsthe location of genes on a chromo-some is called a linkage map.

You have already learned aboutseveral genetic disorders thataffect humans—Huntington’s

disease, cystic fibrosis, Tay Sach’s dis-ease, and sickle-cell anemia. In thelast section, you learned that trans-genic bacteria are being designed totreat disorders such as diabetes anddwarfism. Scientists hope someday to be able to treat more disorders. Toaccomplish this, they aresequencing the entire humangenome. How are theydoing this and what do they hope to accomplish?

SECTION PREVIEW

ObjectivesAnalyze how the effortto completely map andsequence the humangenome will advancehuman knowledge.Predict future applica-tions of the HumanGenome Project.

Vocabularyhuman genomelinkage mapgene therapy

13.3 The Human Genome

Sickled red blood cells(above) and humanchromosomes (inset)

OriginWORDWORD

genomeFrom the Greekword genos, meaning“race.” A genome is the total numberof genes in an individual.

Magnification: 1750�

Magnification: 16 800�

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Section 13.3

PrepareKey ConceptsThe organized effort to map andsequence the human genomeusing DNA technology is pre-sented. Students will also exploreapplications of this project.

Planning■ Obtain a chromosome linkage

map for the Quick Demo.■ Gather the materials for the

Alternative Lab.


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switch

connecting wire

lamp

resistor (such as toaster, stove, iron)

motor

fuse


How could this circuit diagram help an engineer find and repaira problem with the circuit?

How might having a “diagram” of the location of all human genesbe helpful?

11

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GiftedLinguistic Have gifted students lookin recent issues of Science or Science

News and report on the progress of theHuman Genome Project and other DNAtechnology.

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Section Focus Transparency 34and Master

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VIDEODISCThe Infinite VoyageThe Geometry of Life

The Human Genome Project(Ch. 11), 4 min.

!8.8B"

fragment is then individually clonedand sequenced. The cloned fragmentsare aligned in the proper order byoverlapping matching sequences, thusdetermining the sequence of a longerfragment. Automated machines canperform this work, greatly increas-ing the speed of map development. It is expected that the entire human genome may be mapped andsequenced by the year 2003.

Applications of theHuman Genome Project

As chromosome maps are made,how can they be used? Improvedtechniques for prenatal diagnosis ofhuman disorders, use of gene ther-apy, and development of new meth-ods of crime detection are currentareas of research.

Diagnosis of genetic disordersOnce it is clearly understood

where a gene is located and thegene’s DNA sequence is known, adiagnosis of a genetic disorder maybe made before birth. What tech-nique leads to making this diagnosis?The DNA of people with the disor-der is analyzed for common patternsthat appear to be associated with thedisorder. A few cells are obtainedfrom a fetus or from the fluid sur-rounding the fetus. To obtain a largeenough sample of DNA, the cells aregrown in a nutrient medium untilmany cells have formed, a techniqueknown as cell culture. Cells in a cellculture all have the same geneticmaterial; that is, they are clones.Thus, when the cultured fetal cellsare examined and found to haveDNA with the pattern associatedwith the disorder, there is a strongprobability that the fetus will developthe disorder.


CAREERS IN BIOLOGY

Forensic Analyst

Would you like to work in acrime laboratory, helping

police and investigators figure out“who done it?” Then consider acareer as a forensic analyst.

Skills for the JobForensic analysts include identifica-

tion technicians (who work with finger-prints), crime lab technologists (who usemicroscopes, lasers, and other tools to analyze tissue samplesand other evidence), and medical examiners (who performautopsies to determine the cause of death). Most forensicanalysts work in labs operated by the federal, state, or localgovernment. Requirements include on-the-job training fortechnicians, one or more college degrees that include crimelab work for technologists, and a medical degree for medicalexaminers. Analysts hired by the FBI complete an additional14-week training program.

For more careers in related fields, be sureto check the Glencoe Science Web Site.

www.glencoe.com/sec/science

Figure 13.9 Radioactively labeled complementary DNA for the gene to bemapped is made and added to metaphase chromosomes. Thelabeled DNA binds to the gene and indicates its location as a spot.In this photo, six genes are mapped simultaneously.

Career PathCourses in high school:computer science, mathe-

matics, physics, photography, andEnglishCollege: bachelor’s degree orhigher in criminal justice withcrime laboratory workOther education source: on-the-job training for forensic tech-nicians

Career IssueEvery year, new forensic technol-ogy is developed, yet society grad-ually undergoes many other kindsof changes, too. Ask studentswhether a forensic analyst’s job is easier or more difficult than itwas 20 years ago. Explain youranswer.

For More InformationFor more information aboutforensic sciences, write to:

American Academy of ForensicSciences

218 East Cache La PoudreColorado Springs, CO 80903

a bar code in each of four envelopesmarked: blond female, type O blood(matching bar code); blond male, type Bblood; dark-haired male, type O blood; anddark-haired male, type B blood.Procedure

1. Roger Trueblood, dark hair, type Bblood, was shot and killed. You mustfind which suspect is guilty.

2. Rotate to the tables and collect infor-mation. At the last table, decide who is

guilty and open the envelope to see ifthe DNA fingerprint matches that atthe crime scene.

Analysis1. What information did you learn from

the table displays? The clues includedblond hair, type O blood, and femalecheek cells (presence of Barr bodies).

2. How are the bar codes like DNA finger-printing? They are a series of lines ofvarying thickness.

Performance Have students writea report stating their conclusions aboutthe crime. The blond female is guiltybecause her hair, type of blood, and cheek cellswere found at the scene. Use thePerformance Task Assessment List forLab Report in PASC, p. 47. L2

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The historical method used toassign genes to a particular humanchromosome was to study linkagedata from human pedigrees. Recallfrom your study of meiosis thatcrossing over occurs during prophaseI. As a result of crossing over, the off-spring have a combination of allelesnot found in either parent. The fre-quency with which these alleles occurtogether is a measure of the distancebetween the genes. Genes that crossover frequently must be farther apartthan genes that rarely cross over. Thepercentage of these crossed-overtraits appearing in offspring is thenused to determine the relative posi-tion of genes on the chromosome,and thus to create a linkage map.

Because humans have only a fewoffspring compared with the largernumbers of offspring in other speciesand because the generation time is solong, mapping by linkage data isextremely inefficient. Biotechnologyhas now provided scientists with newmethods of mapping genes. By atechnique called polymerase chainreaction (PCR), millions of copies oftiny DNA fragments are cloned in amatter of a few hours. Scientists cancopy the DNA from thousands ofseparate sperm cells produced by oneindividual and analyze the results ofcrossing over that occurred duringthe meioses that produced the sperm.Instead of examining actual offspring,they examine sperm cells—hundredsand even thousands of potential off-spring—to create linkage maps.Another method of mapping chro-mosomes is shown in Figure 13.9.

Sequencing the human genomeThe difficult job of sequencing the

human genome is accomplished bycleaving samples of DNA into frag-ments using restriction enzymes, asdescribed earlier in this chapter. Each


Storing the HumanGenome It has been esti-mated that the humangenome consists of threebillion nitrogen basepairs. How much roomwould all of the geneticinformation in a singlecell take up if it wereprinted in a book the sizeof a typical novel?

Procedure! Copy the right column

of the data table marked “Letters and numbers.”@ Select a random page from a novel.# Follow the directions in the table. Record your calcula-

tions in your data table.

Analysis1. What changes could be taken to improve the accuracy of

this activity at steps A-C?2. What assumption is being made at step G?3. Explain the logic for step D.4. a. How many books the size of your novel would be

needed to store the human genome?b. How many books the size of your novel would be

needed to store a typical bacterial genome? Assumethere are three million base pairs in the genome of abacterium.

MiniLab 13-2MiniLab 13-2 Using Numbers

DirectionsLetters andnumbers

A. Count the number of characters (letters, punctuation marks, and spaces) across oneentire line of your selected page.

B. Count the number of lines on the page.

C. Calculate the number of characters on thepage. (Multiply A � B.)

D. Let one nitrogen base equal one character.Knowing that DNA is made of nitrogen basepairs, divide C by 2.

E. Record the number of pages in your novel.

F. Calculate the number of base pairs in yournovel. (Multiply E � D.)

G. Calculate the number of books the size of your novel needed to hold the human genome. (Divide 3 billion by F.)

Data Table

2 Teach

Alternative LabCrime Analysis

Purpose Students will solve a crime using humangenetics and DNA technology.Materials glass slide, red juice, 5 bar codes (2 thatmatch), 2 strands of human hair (blond anddark), T-shirt with spot of red ink, stained

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slide of female cheek cells, microscopePreparationTable 1: hair from the scene. Table 2: shirtwith a blood stain (red ink) and a slide withtwo drops of juice to represent blood typ-ing (no clotting with the addition of anti-Aand anti-B sera). Table 3: slide of stainedcheek cells with microscope pointer on aBarr body. Table 4: bar code representingthe DNA fingerprint of blood from thecrime scene (one of two that match). Place358

MiniLab 13-2MiniLab 13-2

Purpose Students will use an ana-logy to calculate the size of

the human genome.

Process Skillsacquire information, interpretdata, think critically, use numbers

Teaching Strategies■ Go through calculationswith students. Place the datatable on an overhead projector as you work through each step.■ To provide consistency of data,photocopy a page from a noveland allow all students to use it togather their initial data. Advisethem of the total number ofpages in the book.

Expected ResultsSample data: A = 80; B = 45; C = 3600; D = 1800; E = 400; F = 720 000; G = 4167

Analysis1. Take an average of several

pages to arrive at total num-ber of characters per page.

2. The human genome is madeup of 3 billion bases.

3. DNA bases are paired (A-T,C-G). Thus, the totalgenome is expressed in pairsso the number of charactersmust be expressed in pairs.

4. a. 4167 books b. 4.17 books

Portfolio Have studentscalculate the number of base pairson each chromosome, assumingthat all chromosomes are the samelength. Use the Performance TaskAssessment List for Using Mathin Science in PASC, p. 29. L2

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CAREERS IN BIOLOGY


Visual-Spatial Show students a human chro-

mosome map so they can seehow many genes have beenmapped. Such maps havebeen published by Sciencemagazine.

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electrophoresis and compared withthose obtained from a crime scene.

Chromosomes consist of genes thatare separated by segments of noncod-ing DNA, DNA that doesn’t code forproteins. Both the genes and the non-coding segments follow fairly stan-dard patterns from person to person,but there is also a distinct pattern ineach individual—so distinct, in fact,that DNA patterns can be used likefingerprints to identify the person (orother organism) from whom theycame. DNA fingerprinting worksbecause no two individuals (exceptidentical twins) have the same DNAsequences, and because all cells(except gametes) of an individual havethe same DNA. You can read about areal example of DNA fingerprintingin the Problem-Solving Lab.

PCR techniques have been used toclone DNA from many sources.Geneticists are cloning DNA frommummies and analyzing it in order tobetter understand ancient life.Abraham Lincoln’s DNA has beentaken from the tips of a lock of hishair and studied for evidence of apossible genetic disorder. The DNAfrom fossils has been analyzed andused to compare extinct species withliving species, or even two extinctspecies with each other. The uses ofDNA technology are unlimited.



Understanding Main Ideas1. What is the Human Genome Project? 2. Compare a linkage map and a sequencing map. 3. What is gene therapy? 4. Explain why DNA fingerprinting can be used as

evidence in law enforcement.

Thinking Critically5. Describe some possible benefits of the Human

Genome Project.

6. Observing and Inferring Suppose a cysticfibrosis patient has been treated with gene ther-apy, in which a normal allele is inserted into lungcells of the patient using a virus vector. Does thisperson still run the risk of passing the disorder tohis or her offspring? Explain. For more help, referto Thinking Critically in the Skill Handbook.


How is identification made from a DNA fingerprint?DNA fingerprint analysis requires a sample of DNA from aperson, either living or dead. The DNA is first cut up intosmaller segments with enzymes. The segments are then sepa-rated according to size using electrophoresis. When stained,the DNA segments appear as colored bands in a specificorder. These bands form a person’s DNA fingerprint.

AnalysisAn unidenti-

fied soldier fromthe Vietnam Warwho had beenplaced in the Tombof the Unknownsat ArlingtonNational Cemeterywas identifiedthrough DNA fin-gerprinting. The soldier could have been one of four possibleindividuals. A DNA sample from his body was analyzed. TheDNA from the parents of the four suspected soldiers was ana-lyzed. The diagram shows a DNA fingerprint pattern analysissimilar to the one that was actually done. Find the correctmatch between the soldier’s DNA fingerprint pattern andthose of his parents. Remember, a child’s DNA is a combina-tion of parental DNA.

Thinking Critically1. Which parental DNA matched the unknown soldier? How

did the DNA pattern allow you to decide?2. What percent of the soldier’s DNA matched his father’s

DNA? His mother’s? Explain why.3. Could an exact identification have been made if only one

parent were alive? Explain why.

Problem-Solving Lab 13-3Problem-Solving Lab 13-3 Applying Concepts

SoldierParentsA B C D E F

Parents ParentsG HParents

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3 AssessCheck for UnderstandingAsk students to explain what theHuman Genome Project propos-es to do. map and sequence all thegenes on human chromosomes

ReteachAsk students to list applications ofthe Human Genome Project.diagnosis of genetic disorders, genetherapy, and DNA fingerprinting

ExtensionKinesthetic Cloning kits canbe purchased from biological

supply companies.

Skill Ask students to pre-dict future applications of the Hu-man Genome Project.

4 CloseDiscussionAsk students whether couplesshould be able to change featuresof their unborn children if thefeatures are not disorders, such aseye color, hair color, or gender.

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Section AssessmentSection AssessmentSection Assessment1. an international effort to completely map

and sequence the human genome2. A sequencing map shows the sequence of

DNA bases; a linkage map shows the posi-tion of genes on a chromosome.

3. the insertion of normal alleles into hu-man cells to correct genetic disorders

4. The DNA of every individual, except iden-tical twins, is unique. It can be used to

identify individuals with great accuracy.5. If the location of genes is known, then

gene therapy can be used to replace de-fective genes and cure a disorder.

6. Because only the lung cells had the allelereplaced, the sex cells would still containa cystic fibrosis allele and the disorderwould be passed on to the offspring.

Gene therapyIndividuals who inherit a serious

genetic disorder now have a reason tohope for a bright future—gene ther-apy. Gene therapy is the insertion ofnormal genes into human cells to cor-rect genetic disorders. This technol-ogy has already entered trial stages ina number of attempts to treat or curegenetic disorders; some of the firsttrials were on patients suffering fromcystic fibrosis. The method used inthese trials is shown in Figure 13.10.Doctors hope that copies of the nor-mal gene introduced into the lungs byway of a nasal spray will cause lungcells to produce normal mucus.

Another example of successfulgene therapy is with people affected

by SCID (severe combined immun-odeficiency disease). One particulartype of SCID is caused by a defectin an enzyme within a specific cellin the immune system. Without thenormal enzyme, a substrate of theenzyme builds up in the cells of theimmune system and eventually killsthe cells. The immune system isshut down with the result that inthese patients, even slight colds canbe deadly. In gene therapy for thisdisorder, the cells of the immunesystem are separated from bloodsamples and the functional gene isadded to them. The cells are theninjected back into the patient. Thedrawback with most current formsof gene therapy is that the genedoes not always stay active for verylong periods of time, or the cellsthemselves do not have long lifespans, so the treatments must berepeated often, sometimes everytwo weeks. Still, it seems likely thatthe next decade will see the use ofDNA technology to cure manygenetic disorders.

DNA fingerprintingLaw-enforcement workers use

unique fingerprint patterns to deter-mine whether suspects have been at acrime scene. In the past ten years,biotechnologists have developed amethod that determines DNA fin-gerprints. DNA fingerprinting can beused to convict or acquit individualsof criminal offenses because everyperson is genetically unique.

Small DNA samples can beobtained from blood, hair, skin, orsemen and copied millions of timesusing polymerase chain reactiontechniques. When an individual’sDNA is cleaved with a restrictionenzyme, the DNA is cut into frag-ments of different lengths. DNAfragments can then be separated by


Nasal cell

Cold virus

Lung

Normal CFgene

Normal CF geneinserted into coldvirus vector

Figure 13.10 Gene therapy is oneuse of recombinantDNA technology onthe horizon. Theprocess is simplifiedin this illustration ofgene therapy for acystic fibrosis patient.

360

Purpose Students will analyze DNA fin-gerprints to determine identity ofan unidentified soldier.

Process Skillsthink critically, analyze informa-tion, apply concepts, compare andcontrast, interpret data, interpretscientific illustrations

Teaching Strategies■ Advise students that photos ofDNA fingerprints are X rays ofelectrophoresis results. TheDNA is treated with radioactivedyes that expose X-ray film.■ Remind students that eachperson has unique DNA (exceptfor identical twins). Each con-tains DNA from both parentalDNA. Ask them to recall thenumber of chromosomes con-tributed at fertilization by eachparent to future offspring.■ Photocopy the diagram forstudent use so that they do notwrite in the book.■ Suggest that a ruler be placedalong the bottom edge of eachband for ease in matching.

Thinking Critically

1. Parents C and D; half of thesoldier’s DNA matched par-ent C and the other halfmatched parent D.

2. 50% from each parent; eachparent contributes half oftheir DNA to an offspring.

3. Yes, the soldier’s DNA wouldstill match the living parent’shalf.

Knowledge Ask students:Could the unidentified soldier beidentified if he were adopted? notunless his birth parents are knownCan the unknown soldier fromWW I be identified throughDNA technology? Not likely; hisparents must be deceased. Use thePerformance Task AssessmentList for Writing in Science inPASC, p. 87. L1

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Problem-Solving Lab 13-3Problem-Solving Lab 13-3

PortfolioPortfolio

BioethicsAsk students to write an essay giving theiropinions on whether parents shouldchange a child’s genes before birth foreach of the following: to correct a child’sgenetic disorder, to make a child moreattractive, to change the child’s gender.P

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Gene TherapyLinguistic Have students researchthe current progress being made on

gene therapy in the treatment of cysticfibrosis or other genetic disorders. Theycan then write reports to include in theirjournals.

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Concept Mapping, p. 13

Critical Thinking/ProblemSolving, p. 13

BioLab and MiniLab Work-sheets, pp. 63-64

Reinforcement and StudyGuide, p. 58

Content Mastery, pp. 63-64

Tech Prep Applications, pp. 21-22 L2

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G G A T C C

C C T A G G

G G A T C C

C C T A G G

G G A T C C

C C T A G G

–G

–G

– A– T – C – C –

–G

–G

–A

–T

–C

–C

–

– C– C

– T–A–G–G–

–C –C–T

–A–G

–G–

about 5 cm apart on the longerstrip of paper.

-G-G-A-T-C-C--C-C-T-A-G-G-

5. After coloring the shorter strip ofpaper and writing the sequenceon it, tape the ends together.

6. Assume that a particular restric-tion enzyme is able to cleaveDNA in a staggered way as illus-trated here.

-G G-A-T-C-C--C-C-T-A-G G-

Cut the longer strand of DNA inboth places as shown. You nowhave a cleaved foreign DNA frag-ment containing a gene that canbe inserted into the plasmid.

7. Once the sequence containing theforeign gene has been cleaved,cut the plasmid in the same way.

8. Splice the foreign gene into theplasmid by taping the papertogether where the sticky endspair properly. The new plasmidrepresents recombinant DNA.


1. Comparing and Contrasting Howdoes the paper model of a plasmidresemble a bacterial plasmid?

2. Comparing and Contrasting Howis cutting with the scissors differentfrom cleaving with a restrictionenzyme?

3. Thinking Critically Enzymes thatmodify DNA, such as restrictionenzymes, have been discoveredand isolated from living cells.What functions do you think theyhave in living cells?

ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

Gene splicing

Plasmid

Restriction enzyme

Sticky ends

Recombinant DNA

BioLab modelTerm

Data Table

Going FurtherGoing Further

Project Design and construct a three-dimensional model that illustrates theprocess of preparing recombinant DNA.Consider using clay, plaster of Paris, or othermaterials in your model. Label the modeland explain it to your classmates.

To find out more aboutrecombinant DNA, visit

the Glencoe Science Web Site.www.glencoe.com/sec/science

- -

9. Copy the data table. Relate thesteps of producing recombinantDNA to the activities of the mod-eling procedure by explaininghow the terms relate to themodel.


1. It is a small circular piece ofDNA.

2. The scissors can cut theDNA anywhere, but therestriction enzyme recognizesa particular sequence.

3. These enzymes may functionin a cell by cutting up anddestroying invading viralDNA.

Performance Have stu-dents write a paragraph summa-rizing what they have learnedabout the use of restrictionenzymes. Have students explainhow the BioLab model is like theterms listed in the data table. Usethe Performance Task AssessmentList for Writing in Science inPASC, p. 87.


ANALYZE AND CONCLUDEANALYZE AND CONCLUDE

363

Going FurtherGoing Further

Kinesthetic Studentscould use different colors

of clay, or use food coloring todye plaster of Paris, to showrecombinant DNA in their models.

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Modeling Recombinant DNA

Experimental procedures have been developed that allow recombinantDNA molecules to be engineered in a test tube. From a wide variety

of restriction enzymes available, scientists choose one or two that recognizeparticular sequences of DNA within a longer DNA sequence of a chro-mosome. The enzymes are added to the DNA, which is cleaved at therecognition sites. Because the cleaved fragments have ends that are avail-able for attachment to complementary strands, the fragments can beadded to plasmids or to viral DNA that has been similarly cut. When thefragment has been incorporated into the DNA of the plasmid or virus, itis called recombinant DNA.


ProblemHow can you model recombinant

DNA technology?

ObjectivesIn this BioLab, you will:■ Model the process of preparing

recombinant DNA.■ Analyze a model for preparation of

recombinant DNA.

Materialswhite papercolored pencils, red and greentapescissors

Safety PrecautionsAlways wear goggles in the lab. Be

careful with sharp objects.

Skill HandbookUse the Skill Handbook if you need

additional help with this lab.

PREPARATIONPREPARATION

1. Cut a lengthwise strip of paperfrom a sheet of white paper into arectangle about 3 cm by 28 cm.This strip of paper represents along sequence of DNA contain-ing a particular gene that youwish to combine with a plasmid.

2. Cut another lengthwise strip ofpaper into a rectangle about 3 cm

by 10 cm. When taped into aring, this piece of paper will rep-resent a bacterial plasmid.

3. Use your colored pencils to colorthe longer strip red and theshorter strip green.

4. Write the following DNAsequence once on the shorterstrip of paper and two times

PROCEDUREPROCEDURE


Time Allotment One class period

Process Skillscompare and contrast, observeand infer, recognize cause andeffect

Safety PrecautionsBe careful with sharp edges ofscissors. Always cut away from thebody.

■ Review the chemical structureof DNA from Chapter 11before students begin theBioLab.

■ Additional background mater-ial on modeling recombinantDNA can be found in the arti-cle, “Recombinant PaperPlasmids” by Christie L.Jenkins, The Science Teacher,April 1987. You may wish toread this article before youteach the BioLab.

PREPARATIONPREPARATION

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PROCEDUREPROCEDURE

Teaching Strategies■ Students can do this lab alone or withpartners.■ If red and green colored paper is avail-able, then colored pencils will not be neces-sary.■ If you make cardboard models of DNAbases for the Meeting Individual Needs onpage 350, use them in this BioLab.

Data and ObservationsData for completing the table should be asfollows: Gene splicing—process of tapinggreen and red paper together; Plasmid—green strip; Restriction enzyme—scissors;Sticky ends—cut ends on paper; Recom-binant DNA—red and green strips tapedtogether.


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Animation: Recombinant DNADisc 2


Chapter 13 AssessmentChapter 13 Assessment

SUMMARYSUMMARY

Section 13.1

Section 13.2

Section 13.3

Main Ideas■ Geneticists use test crosses to determine the

genotypes of individuals and the probability thatoffspring will have a particular allele.

■ Plant and animal breeders use genetics to selec-tively breed organisms with desirable traits.

Vocabularyinbreeding (p. 346)test cross (p. 347)Applied

Genetics

Main Ideas■ Scientists have developed methods to move

genes from one species into another. Thisprocess uses restriction enzymes to cleave oneorganism’s DNA into fragments and otherenzymes to splice the DNA fragment into aplasmid or viral DNA. Transgenic organismsare able to manufacture genetic products for-eign to themselves using recombinant DNA.

■ Genetic engineering has already been applied tobacteria, plants, and animals. These organismsare engineered to be of use to humans.

Vocabularyclone (p. 352)gene splicing (p. 352)genetic engineering

(p. 349)plasmid (p. 351)recombinant DNA

(p. 349)restriction enzyme

(p. 350)transgenic organism

(p. 349)vector (p. 351)

Main Ideas ■ International efforts are presently underway to

sequence the DNA of the entire human genomeand to determine the chromosome location forevery gene.

■ Applications of the Human Genome Projectinclude the goals of detecting, treating, and curing genetic disorders. DNA fingerprintingcan be used to identify persons responsible forcrimes and to provide evidence that certain persons are not responsible for crimes.

Vocabularygene therapy (p. 360)human genome (p. 357)linkage map (p. 357)

CHAPTER 13 ASSESSMENT 365

1. What is the purpose of a test cross?a. produce offspring that consistently exhibit

a specific traitb. check for carriers of a traitc. explain recessivenessd. show polygenic inheritance

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS 2. Two closely related cattle are mated. Theiroffspring are ________.a. vectors c. mutantsb. carriers d. inbred

3. A section of mouse DNA is joined to a bacte-rial plasmid. The DNA formed is ________.a. translated DNA c. recombinant DNAb. restricted DNA d. transcripted DNA

RecombinantDNA

The HumanGenome

T

A

GGC C T A

GG T C C

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Chapter Assessment, pp. 73-78MindJogger VideoquizzesComputer Test BankBDOL Interactive CD-ROM, Chapter 13

quiz

Main IdeasSummary statements can be used bystudents to review the major con-cepts of the chapter.

Using the VocabularyTo reinforce chapter vocabulary, usethe Content Mastery Booklet andthe activities in the Interactive Tutorfor Biology: The Dynamics of Life onthe Glencoe Science Web Site.www.glencoe.com/sec/science

1. b2. d3. c

UNDERSTANDING MAIN IDEASUNDERSTANDING MAIN IDEAS

All ChapterAssessment

questions and answers have beenvalidated for accuracy and suitabili-ty by The Princeton Review.

When an egg is fertilized by a sperm, azygote is formed that rapidly divides into

a multicellular embryo. During the very earlystages of development, all the genes present ineach embryo cell are functional, or turned on. Atthis point, each embryo cell has the capacity todevelop into a separate and complete individual.But during later stages of development, as theembryo grows into a fetus, its cells begin to dif-ferentiate. They become specialized for differenttasks. Liver cells become distinct from musclecells. Skin cells become different from bloodcells. Once a cell has become specialized, most ofits genes turn off and stop functioning. Only thegenes needed to operate that particular kind ofcell remain turned on, and the cell can no longerperform any other tasks. Because all the cells ofan adult animal are specialized, cloning an animalfrom an adult cell requires finding a way to turnon all the genes in the cell.

A sheep called Dolly Dolly, a lamb born inScotland in February 1997, was the first mammalto be cloned from an adult cell. To produceDolly, researchers took an udder cell from a full-grown ewe, a female sheep. They used an electriccharge to force the udder cell to fuse with anunfertilized sheep egg cell from which thenucleus had been removed. The electric chargecreated openings in the membrane of the egg celllarge enough to admit the udder cell. The fusedcell began to divide and develop into an embryo.The embryo was implanted into the uterus ofanother sheep, which gave birth to Dolly severalmonths later. The method worked, but it took277 cloning attempts to produce a single lamb.Since Dolly was cloned, mice and other animalshave been cloned by slightly different techniques.These new techniques are much more efficient.

Applications for the FutureCloning experiments help to increase our

knowledge of how genes and cells operate.Learning how specific genes are turned on andoff can provide clues about how a fetus growsand develops. It may also contribute to ourunderstanding of genetic diseases. For example,if the activity of a particular gene is found to beresponsible for a disease, scientists could treatthe disease by turning off the gene. Cloningtechniques could also be used to change thefunction of a cell, such as altering skin cells tocreate blood cells for a transfusion or to growbone or cartilage to replace damaged tissue.


How to Clone a Mammal

A cloned organism has exactly the same genes as its parent. A single cell from the parent is usedto produce the clone. During the 1980s and early 1990s, the first successful clones of mammalswere produced from embryo cells of mice, sheep, cattle, goats, rabbits, and monkeys. Creating a

clone from an adult mammal cell proved to be more difficult, but was achieved in 1997.

TechnologyTechnologyBIOBIO

Analyzing Concepts Do you think the genes inthe fused cell that produced Dolly were turnedon or turned off? Explain.

To find out more about genetictechnology, visit the Glencoe

Science Web Site.www.glencoe.com/sec/science

INVESTIGATING THE TECHNOLOGYINVESTIGATING THE TECHNOLOGY

Cloned mice

364

Purpose Students learn about the tech-nique used to produce the firstsuccessful clone of an adult mam-mal and are introduced to some ofthe potential benefits of cloningtechnology.

BackgroundFrogs were the first vertebrateanimals to be cloned. During the1950s and 1960s, scientists evenmanaged to clone adult frogs, butnone of the clones survived pastthe tadpole stage. Clones of mam-mals may have the same genes,but they are not necessarily iden-tical. The uterine environment inwhich an individual develops, andthe conditions under which it israised, have a profound effect onits appearance and behavior.Identical twins may actually bemore alike than clones becausethey share the same uterine envi-ronment and are usually raisedunder the same conditions.

Teaching Strategies■ Review with students the stepsin the reproductive process. Anegg cell and sperm cell each con-tain half the normal complementof chromosomes. When fertiliza-tion occurs, the two cells fuse toform a zygote with a full comple-ment of chromosomes. Thezygote divides by mitosis to forma multicellular embryo. As theembryo grows, cell division con-tinues and the cells begin to dif-ferentiate as the body systems areformed. When all body systemsare present, the embryo becomesa fetus. The fetus continues togrow and develop until it ismature enough to survive outsidethe mother’s uterus.

Investigating the TechnologyThe genes had to be turned on inorder for all organs and systemsto develop.

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TechnologyTechnologyBIOBIO

Going FurtherGoing FurtherGoing Further

Encourage students to research the latestdevelopments in cloning technology andits uses in medicine and other industries.Invite them to discuss or write about ethi-cal issues arising from the development ofcloning.

VIDEOTAPEMindJogger Videoquizzes

Chapter 13: Genetic TechnologyHave students work in groups as they playthe videoquiz game to review key chapterconcepts.




CHAPTER 13 ASSESSMENT 367

24. Observing and Inferring Explain why theuse of bacterial plasmids for gene splicingdoes not interfere with normal cell functionssuch as growth and reproduction.

25. Recognizing Cause and Effect How mayusing biotechnology to engineer many differ-ent transgenic organisms of a given speciesalter the course of evolution for that species?

26. Sequencing Once a foreign gene has beeninserted into a plasmid to form a recombi-nant plasmid, what would be the next step ifyou were to continue the model of recombi-nant DNA technology?

27. Interpreting Data If all human genes havesimilar patterns, how can DNA fragmentsfrom hair or skin be used to identify distinctindividuals by DNA fingerprinting?

28. Concept Mapping Complete the conceptmap by using the following vocabularywords: genetic engineering, transgenicorganisms, restriction enzymes, vector, plasmid, gene splicing.

THINKING CRITICALLYTHINKING CRITICALLY ASSESSING KNOWLEDGE & SKILLSASSESSING KNOWLEDGE & SKILLS

The following graph shows the results of anexperiment using natural and bioengineeredbacteria of the same species that can breakdown oil. Each culture had 40 mL of oiladded on Day 1.

Interpreting Data Use the graph to answerthe following questions.1. Approximately how much oil had been

converted into harmless products by thenatural bacteria after four weeks?a. 4 mL c. 24 mLb. 14 mL d. 40 mL

2. How much oil had been converted bybioengineered bacteria after four weeks?a. 4 mL c. 28 mLb. 14 mL d. 40 mL

3. How much more efficient are the bio-engineered bacteria than the naturallyoccurring species?a. 1� c. 2�b. 1.5� d. 3�

4. Interpreting Data How can this tech-nology be applied to an oil spill?

For additional review, use the assessmentoptions for this chapter found on the Biology: TheDynamics of Life Interactive CD-ROM and on theGlencoe Science Web Site.www.glencoe.com/sec/science

CD-ROM

Weeks

Natural bacteria

Bioengineeredbacteria

mL

of o

il

1 2 3 410

20

30

40

Breakdown of Oil by Bacteria

and used in

is an example of a

A

which is cut by

1.

2.

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4.

5.

6.

367

24. Plasmids used for gene splicingare not part of the cells’ chro-mosome. Thus, they can bespliced and manipulated with-out affecting normal cell func-tions.

25. If many alleles were to be trans-ferred into the normal popula-tion, their frequency wouldchange. This would affect thegenetic makeup of the popula-tion.

26. The recombinant DNA is thentransferred into a host cell.

27. DNA fingerprinting uses thesegments of noncoding DNA,which are in distinct, individualpatterns.

28. 1. Plasmid; 2. Vector; 3. Restric-tion enzymes; 4. Genetic engi-neering; 5. Transgenic organ-isms; 6. Gene splicing

THINKING CRITICALLYTHINKING CRITICALLY


1. b2. c3. c4. Because these bacteria

have the ability to digestoil into a harmless prod-uct, the bacteria could beadded to oil spills to cleanthem up quickly.


4. When a bacterial plasmid transfers a piece offoreign DNA to a host cell, the plasmidserves as a(n) ________.a. transgenic cell c. vectorb. hybrid d. enzyme

5. The goal of gene therapy is to insert a________ into cells to correct a genetic disorder.a. recessive allele c. dominant alleleb. growth hormone d. normal allele

6. ________ are genetically identical copies ofDNA.a. Vectors c. Clonesb. Plasmids d. Spliced genes

7. Plant cells are difficult to genetically engi-neer because they do not have the ________needed for taking up foreign DNA.a. amino acids c. clonesb. plasmids d. enzymes

8. The process of gel electrophoresis separates________ fragments by using an electric field.a. DNA c. gelb. cell d. enzyme

9. An organism that contains functional recom-binant DNA is called a ________ organism.a. cleaved c. transgenicb. cloned d. spliced

10. Restriction enzyme EcoR1 cuts DNA strands,leaving ________ ends.a. sticky c. bluntb. smooth d. spliced

11. ________ usually increases the appearance ofgenetic disorders.

12. ________ is a method used to determine theorder of the DNA nucleotides.

13. A ________ occurs when the same sequenceof bases, running in opposite directions, isfound on both DNA strands.

14. ________ cells are the primary source of theplasmids used in DNA technology today.

15. EcoR1 restriction enzyme recognizes thesequence GAATTC in double-strandedDNA. ________ pieces of DNA would resultif EcoR1 were added to the following DNA.

16. The technique ________ is used to make mil-lions of copies of DNA fragments.

17. A gene gun is used to deliver a mechanicaltype of ________.

18. The genetic map that shows the location ofgenes on a chromosome is a ________ map.

19. Cells in a cell culture all have the samegenetic material because they are ________.

20. The Punnett square to the right illustrates a ________.

21. What is the potential use of a map showingthe sequence of DNA bases in a human chro-mosome?

22. Why might it be important to be able to havea human gene expressed in a bacterium?

23. Assume that transgenic organisms can bedeveloped to speed the conversion of nitro-gen from the air into nitrates that plants canuse as fertilizer. How might use of this organ-ism affect an ecosystem?

APPLYING MAIN IDEASAPPLYING MAIN IDEAS

366 CHAPTER 13 ASSESSMENT

TEST–TAKING TIPTEST–TAKING TIP

Let Bygones Be Bygones Once you have read a question, considered theanswers, and chosen one, put that question be-hind you. Don’t try to keep the question in theback of your mind, thinking that maybe a betteranswer will come to you as the test continues.

A

T

A

T

A

T

A

TC

G

C

G

C

G

A

T

A

T

A

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A

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a

Aa Aa

aa

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a

a aa

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4. c5. d6. c7. b8. a9. c

10. a11. Inbreeding12. DNA sequencing13. palindrome14. Bacterial15. Three16. cloning or PCR17. vector18. linkage19. clones20. test cross

21. treating and curing humangenetic disorders

22. Bacteria are capable of makinglarge quantities of human pro-teins when they carry humangenes. These proteins havepotential medicinal and indus-trial usages.

23. This may upset the balancebetween the natural nitrogen-converting bacteria and theplants, possibly disrupting thesoil ecosystem. Plant growthwould increase because nitro-gen is usually a limiting factor.

APPLYING MAIN IDEASAPPLYING MAIN IDEAS



Meiosis Meiosis produces gametes that contain only

one copy of each chromosome instead of two.Some stages of meiosis are similar to those of mito-sis, but in meiosis, homologous chromosomes cometogether as tetrads to exchange genes during aprocess called crossing over. Meiosis also provides a mechanism for rearranging the genetic informa-tion carried by cells. Both crossing over and therearrangement of genes during meiosis producegenetic variability, which may give offspring a sur-vival advantage if the environment changes.

Genetics

369

BIODIGESTBIODIGEST

VITAL STATISTICSVITAL STATISTICS

Mendel’s Ratios of Inherited TraitsSeed Color 3:1 Yellow 6022,

Green 2001Flower Position 3:1 Lateral 651,

Terminal 207Pod Color 3:1 Green 428,

Yellow 152Pod Shape 3:1 Inflated 882,

Constricted 299

Meiosis I

Metaphase I

Metaphase II

Prophase I

Prophase II

Interphase

Telophase II

Telophase IAnaphase II

Anaphase IMeiosis II

Meiosis consists of two divisions, meiosis I and meiosis II. Duringmeiosis I, the homologous chromosomes separate from eachother. In meiosis II, the sister chromatids of each chromosomeseparate from each other.

369

2 Teach

Skill Have students calcu-late the ratios from Men-del’s data as listed in theVital Statistics box. Ask stu-

dents why the ratios are not exact-ly 3:1.

DiscussionHave students discuss Mendelianinheritance. Begin by comparingand contrasting genotype andphenotype. What are the possiblegenotype(s) of a dominant trait? Arecessive trait? A genotype is thealleles for a trait that an individualpossesses. A phenotype is the physicalappearance of that trait. The possiblegenotypes of a dominant trait arehomozygous, PP, or heterozygous, Ppfor the purple flower color. A recessivetrait must be homozygous, pp, for therecessive phenotype.

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ActivityVisual-Spatial Have studentsdraw a cell undergoing

meiosis. Make sure they labelhomologous chromosomes andsister chromatids.

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BIODIGESTBIODIGEST

FOCUS ON HISTORYFOCUS ON HISTORY

To investigate the genetic inher-itance of pea plant traits, the

Austrian monk Gregor Mendelused critical thinking skills todesign his experiments. When hecollected data, he considered notonly the qualitative characteristics,

such as whether the plants were tall or short, but also the quantitative

data by analyzing the ratios of tall toshort plants in each generation. Mendelobserved that there were two variations

for each trait, such as tall and shortplants. He formed the hypothesis thatalleles transmitted these traits fromone generation to the next. Afterstudying several traits for many genera-tions, Mendel formed two laws. Thelaw of segregation states that the twoalleles for each trait separate whengametes are formed. The law of inde-pendent assortment states that genesfor different traits are inherited inde-pendently of each other.

Mendel

368

GeneticsGenetics is the study of inheritance. The physical traits, or

phenotype, of an individual are encoded in small segmentsof chromosomes called genes. Not all genes are expressed as aphenotype. Therefore, the genotype, the traits encoded in thegenes, may be different from the expressed phenotype.

For a preview of the genetics unit, study this BioDigest before you read the chapters.After you have studied the genetics chapters, you can use the BioDigest to review the unit.

BIODIGESTBIODIGEST

When a PP purple pea plant is crossed with app white plant, all the offspring are purple,Pp. When two Pp plants are crossed, three-fourths of the plants in the next generationwill be purple and one-fourth will be white.

Purple (PP)

PP Pp Pp pp

All purple flowers (Pp)

3 purple:1 white

White (pp)

Simple MendelianInheritance

A trait is dominant if only one allele of agene is needed for that trait to be expressed. Iftwo alleles are needed for expression, the trait issaid to be recessive. In pea plants, the allele forpurple flowers is dominant and the allele forwhite flowers is recessive. Any plant with PP or Ppalleles will have purple flowers. Any plant withpp alleles will have white flowers.

Gregor Mendel

Chromosomes


368

National Science Education StandardsUCP.1, UCP.2, UCP.3, UCP.5,C.1, C.5, E.2, F.1, F.5, F.6, G.1,G.3

PreparePurposeThis BioDigest can be used as anintroduction to or as an overviewof genetics. If time is limited, youmay wish to use this unit summa-ry to teach genetics in place of thechapters in the Genetics unit.

Key ConceptsStudents will learn about Mendeland his insights into heredity. Theprocess by which genetic infor-mation is copied and proteins areformed by the genetic code isdescribed. Finally, the patterns ofhuman heredity and DNA tech-nology are discussed.

1 FocusBellringer

Visual-Spatial Have studentsclosely examine the flower

of a pea plant so they can becomefamiliar with the materials withwhich Mendel worked.

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BIODIGESTBIODIGEST

MultipleLearningStyles

Look for the following logos for strategies that emphasize different learning modalities.

Kinesthetic Quick Demo, p. 372;Meeting Individual Needs, p. 372Visual-Spatial Bellringer, p. 368;Quick Demo, p. 369; Activity,

p. 369; Demonstration, p. 371;Portfolio, p. 371

Intrapersonal Extension, p. 373Linguistic Biology Journal,p. 370


Visual-Spatial Draw a Punnett square for

another cross of Mendel’s ex-periments mentioned in theVital Statistics box. Correlatethis to the pea crosses for petalcolor. Ask students whetherthe ratios of offspring are thesame.

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Exploration: Trait InheritanceExploration: Punnett SquareAnimation: MeiosisDisc 2

Assessment PlannerAssessment Planner

Portfolio AssessmentPortfolio, TWE, p. 371

Knowledge AssessmentAssessment, TWE, p. 373BioDigest Assessment, SE, p. 373

Skill AssessmentAssessment, TWE, p. 369

AUGA

A

U

U

G AAG U GCUC

C

C A A

Methionine

Alanine

AUGA U

U

G AA

A

G U GCUC

C

C A A

G UC

Stopcodon

AA

A A

U UGA U G AAG UU

C

C

C A A

Flower color in snapdragons is an exam-ple of incomplete dominance. The flowercolor of the heterozygote is intermediateto that of the two homozygotes.

TranslationA codon, a sequence of three bases in the

mRNA, serves as a code for an amino acid. In aprocess called translation, a ribosome “reads” thecodons on the molecule of mRNA. Transfer RNA(tRNA) molecules bring the appropriate aminoacids to the mRNA at the ribosome. The aminoacids are bonded together to form a protein.

Genetics

371

BIODIGESTBIODIGEST

In translation, the sequence of bases inthe mRNA is translated into a sequence ofamino acids in a protein chain. Every threenucleotides code for a specific amino acid.

In any mating between humans, half theoffspring will have the XX genotype, whichare females, and half the offspring willhave the genotype XY, which are males.

XXFemale

XXFemale

Mother’schromosomes

X

X Y

X

XYMale

Father’s chromosomes

XYMale

Complex InheritancePatterns

An incomplete dominance pattern of inheri-tance produces an intermediate phenotype in theheterozygote. In codominant inheritance, theheterozygote expresses both alleles. Some traits,such as human blood types, are governed by mul-tiple alleles, although any individual can carryonly two of those alleles.

All pink

Red White

11

22

33

371

Visual Learning Put up an overhead of translationand ask students questions. Have them differentiate betweenmRNA and tRNA. Give studentsa sequence of several mRNA co-dons and ask them to “translate”the RNA bases into an amino acidsequence. mRNA contains a copy ofa gene from DNA. tRNA carriesamino acids to ribosomes.

DemonstrationVisual-Spatial Grow red,white, and pink snapdragons.

Ask students to draw Punnettsquares for various matings of thesnapdragons. Have them identifythis trait as incomplete domi-nance.

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BIODIGESTBIODIGEST

Producing Physical Traits

Deoxyribonucleic acid (DNA) is a double-stranded molecule made up of a sequence ofnucleotide base pairs that encode each gene on achromosome. There are four bases in DNA: A, T,C, and G. Because of their molecular shape, A canpair only with T, and C can pair only with G. Thisprecise pairing allows the DNA molecule to copyitself in a process called DNA replication.

TranscriptionTo make a protein, the segment of DNA con-

taining the gene for that protein must be tran-scribed. First, the sequence of bases in the DNAsegment is copied into a molecule of messengerribonucleic acid (mRNA), which then moves fromthe nucleus to the cytoplasm. RNA is similar toDNA except that RNA is single-stranded and con-tains the base U in place of T.

FOCUS ON ADAPTATIONSFOCUS ON ADAPTATIONS

Some recessive alleles, such as the sickle-cell allele,remain in a population because they give the het-

erozygote a genetic advantage in certain environ-ments. Sickle-cell anemia affects red blood cells so thatthey change shape when oxygen levels are low, block-ing blood vessels. The disorder is prevalent in Africa,where malaria is common. When individuals who areheterozygous for the sickle-cell trait contract malaria,they suffer fewer and milder symptoms of malaria,whereas normal individuals who contract malaria maydie. Therefore, sickle-cell alleles in heterozygotesremain in the population.

Heterozygote Advantage

Genetics

370

BIODIGESTBIODIGEST

22

A

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TC

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U U U UC C CA A A AG

11

33

RNA

RNA

DNA

DNA

In transcription, the twostrands of DNA separateand a molecule of mRNA is made according to thesequence of bases in theDNA. After transcription,the mRNA strand leavesthe nucleus to travel to theribosomes in the cytoplasm.

In sickle-cellanemia, redblood cells forma sickle shapecompared to theround shape ofnormal redblood cells.



370

Visual Learning Put up an overhead of transcrip-tion and ask students questionsabout the process. Ask them todefine a gene, transcription, andmRNA. Have them identify thebases of DNA. A gene is a segmentof DNA containing the informationfor making a protein. Transcriptionis the process whereby a DNAsequence of bases is copied into asequence of bases in mRNA. mRNAwill carry the information for pro-teins into the cytoplasm. The bases ofDNA are adenine, thymine, cytosine,and guanine.

DiscussionDiscuss the idea that some traitssuch as sickle-cell anemia mayconfer an advantage for survivalto a heterozygote. How mightthis idea have been used through-out evolution to define character-istics of living species? Traits thatconfer an advantage to individuals ina species increase the chances of thatindividual surviving to reproduceand pass on the traits.

BIODIGESTBIODIGEST


Mendel’s ExperimentsLinguistic Have students writeabout Mendel’s experiments and his

conclusions. How did he follow the scien-tific method in testing his hypotheses?What two laws did he derive from hisstudies?

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PortfolioPortfolio

Punnett SquaresVisual-Spatial Make Punnettsquares demonstrating various

crosses between individuals with a domi-nant trait, a recessive trait, incompletedominance, codominance, and a sex-linked trait.

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CD-ROMBiology: The Dynamics of LifeAnimation: DNA Replication

Animation: DNA TranscriptionAnimation: TranslationBioQuest: Building a ProteinDisc 2


Sex-Linked Traits (Ch. 35)Disc 1, Side 1, 1 min. 49 sec.

Fruit Fly Genetics (Ch. 34)Disc 1, Side 1, 50 sec.

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Gene TherapyGene therapy involves the

insertion of normal alleles intohuman cells to correct genetic dis-orders. Gene therapy is used totreat cystic fibrosis, a seriousgenetic disorder caused by a miss-ing protein in the cell membrane.In gene therapy for this disorder,the normal allele is inserted into avirus that causes the common cold.The virus carries the gene into thepatient’s cells, which begin to pro-duce the missing protein.

Genetics

373

BIODIGESTBIODIGEST

BIODIGEST ASSESSMENTBIODIGEST ASSESSMENT

Understanding Main Ideas1. An example of a dominant trait is

________.a. cystic fibrosisb. white pea flowersc. purple pea flowersd. sickle-cell anemia

2. The three-nucleotide base sequence that codes for an amino acid is called ________.a. a codon c. tRNAb. a base pair d. mRNA

3. Something that carries a piece of DNA into a host cell is called a ________.a. clone c. vectorb. bacterial cell d. recombinant DNA

4. A base sequence that would be found in RNA but not in DNA is ________.a. ATTCGA c. AUUCCGb. TTTGGC d. TUCCGT

5. A broad range of phenotypes for a given trait is usually the result of ________.a. multiple alleleic inheritanceb. incomplete dominancec. codominanced. polygenic inheritance

6. A base pair that can be found in a DNA molecule is ________.a. A—T c. A—Gb. A—C d. C—C

7. The process of copying DNA into mRNA iscalled ________.a. translation c. replicationb. transcription d. cloning

8. A trait that can be expressed only as ahomozygous genotype is ________.a. dominant c. codominant b. recessive d. X-linked

9. Meiosis differs from mitosis in that the cellsproduced by meiosis have ________ thenumber of chromosomes as the parent cell.a. half c. twice b. three times d. the same as

10. In crossing over, genetic material is ex-changed between ________, resulting ingenetic variability of offspring.a. cells c. genesb. chromatids d. alleles

Thinking Critically1. State Mendel’s law of independent assort-

ment and explain what it means.

2. Compare the phenotypes of the heterozy-gotes in simple Mendelian inheritance,incomplete dominance, and codominance.

3. Describe the process for producing a bac-terium that contains recombinant DNA.

Nasal cell

Cold virus

Lung

NormalCF gene

Normal CF geneinserted into coldvirus vector

In gene therapy for cysticfibrosis, the normal alleleis inserted into a virus thatcan be inhaled through anasal spray.

373

3 AssessCheck for UnderstandingAsk students to define transcrip-tion and translation and to explaineach process.

Reteach Put up an overhead of the stagesof meiosis and ask students toidentify the stages.

ExtensionIntrapersonal Have studentsresearch some of the uses of

genetic technology, such as theproduction of human insulin andhuman growth hormone.

Knowledge Put an exam-ple of incomplete dominance orcodominance on the board andask students to identify the patternof inheritance.

4 CloseDiscussionDiscuss the implications of genetherapy using cystic fibrosis as anexample. Will effective treatmentalter the possibility of passing thistrait to future generations?

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BIODIGESTBIODIGEST

BIODIGEST ASSESSMENTBIODIGEST ASSESSMENT

Understanding Main Ideas1. c 4. c 7. b 9. a2. a 5. d 8. b 10. b3. c 6. a

Thinking Critically1. Each gene on a chromosome will separate

independently of any other gene duringmeiosis.

2. In simple Mendelian inheritance, a heterozy-gote will carry the phenotype of the domi-nant allele. In incomplete dominance, thephenotype will be a blend of that of the twohomozygotes. In codominance, the pheno-type shows the products of both alleles.

3. Restriction enzymes must be used to cut theDNA fragment and the bacterial plasmid.Then the two may be spliced together andinserted into a bacterium.

Foreign DNA(gene for insulin) Recombined

plasmid

Recombinant DNA

Reproduction

Cloned cells with recombinant DNA

InsulinCleavage sites

Plasmid

E. coli

Bacterialchromosome

Bacterialplasmids

The X chromosome, one of two sex chromo-somes, carries many genes, including the genesfor hemophilia and for color blindness. Most X-linked disorders appear in males because theyinherit only one X chromosome. In females, a nor-mal allele on one X chromosome can mask theexpression of a recessive allele on the other Xchromosome. Finally, some traits, such as skincolor, are polygenic—governed by several genes.

Recombinant DNATechnology

To make recombinant DNA, a small segmentof DNA containing a desired gene is inserted intoa bacterial plasmid, a small ring of DNA. The plas-mid acts as a vector to carry the DNA segmentinto a host bacterial cell. Every time the bacter-ium reproduces, the plasmid containing the in-serted DNA is duplicated, producing copies of therecombinant DNA along with the host chromo-some. Because these new DNA segments areidentical to the original, they are called clones.The host cell produces large quantities of the pro-tein encoded by the recombinant DNA it con-

Genetics

372

BIODIGESTBIODIGEST

VITAL STATISTICSVITAL STATISTICS

Frequency of Genetic Disordersin the PopulationCystic Fibrosis: 1 in 2000 white Americans ishomozygous recessive.Sickle-Cell Anemia: 1 in 500 AfricanAmericans is homozygous recessive.Tay-Sachs Disease: 1 in 3600 Jews of east-ern European ancestry is homozygous reces-

Recombinant DNA can be cloned to produce manycopies of a specific segment of DNA. The insetphoto shows crystals of insulin that were purifiedfrom a culture of recombinant bacteria.

372

ReinforcementHave students make a table withthe following headings: Domi-nant, Recessive, Incomplete dom-inance, Codominance, Multiplealleles, Polygenic inheritance, andX-linked traits. Under each head-ing, they should list the following:genotype(s), whether the trait ismore common in males orfemales, one specific examplefrom the text, and how many phe-notypes are possible.

BIODIGESTBIODIGEST


Kinesthetic Take twopieces of electrical wire

of different colors. Use clippersas restriction enzymes to cutthe wires. Peel some of the colored coating from the cutedges of the wires to demon-strate sticky ends. Then splicethe two wires together to sim-ulate recombinant DNA.

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Learning DisabledKinesthetic Have students use a mo-del of a human respiratory system to

simulate gene therapy for cystic fibrosis.Students should show the pathway takenby viral DNA containing a normal allele.P

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VIDEODISCVIDEOTAPEThe Secret of Life

In the Land of Milk andMoney: Biotechnology

Tinkering With Our Genes:Genetic Medicine

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Reinforcement and StudyGuide, pp. 59-60

Content Mastery, pp. 65-68L1

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VIDEODISCThe Secret of LifeRecombinant DNA Segment

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Documents

Chapter 13: Genetic Technology Text...tinue to impact every aspect of your life, from growing the food you eat to treating a dis-ease you might inherit. Genetic Technology in Our Lives