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Analyzing Inheritance

Offspring resemble their parents. Offspring inherit genes for characteristicsfrom their parents. To learn about inheritance, scientists haveexperimented with breeding various plants and animals.In each experiment shown in the table on the next slide, two pea plantswith different characteristics were bred. Then, the offspring produced werebred to produce a second generation of offspring. Consider the data andanswer the questions that follow.

Section 11-1

Interest Grabber

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1. In the first generation of each experiment, how do the characteristics ofthe offspring compare to the parents’ characteristics?

2. How do the characteristics of the second generation compare to thecharacteristics of the first generation?

Section 11-1

Interest Grabber continued

ParentsLong stems × short stems

Red flowers × white flowers

Green pods × yellow pods

Round seeds × wrinkled seeds

Yellow seeds × green seeds

First Generation

All long

All red

All green

All round

All yellow

Second Generation

787 long: 277 short

705 red: 224 white

428 green: 152 yellow

5474 round: 1850 wrinkled

6022 yellow: 2001 green

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11–1 The Work of Gregor MendelA. Gregor Mendel’s PeasB. Genes and DominanceC. Segregation

1. The F1 Cross2. Explaining the F1 Cross

Section 11-1

Section Outline

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Gregor Mendel’s Peas

•Mendel was one of the first scientists tostudy genetics, the scientific study ofheredity.•Mendel carried out his research withordinary garden pea plants.•Peas are self-pollinating , which meansthat sperm cells in pollen fertilize the eggcells in the same flower.•This process is called fertilization.•Mendel used true-breeding pea plantsas the basis of his experiments.

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Mendel’s Experiment•Mendel wanted to produce seeds by joiningthe sperm and egg from different plants.•In order to prevent self-pollination, Mendelcut away the pollen bearing male parts anddusted pollen from another plant onto theflower.•This process is called cross-pollination.•Mendel studied seven different pea planttraits.•A trait is a specific characteristic such asseed color or plant height.

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SeedShape

FlowerPosition

Seed CoatColor

SeedColor

PodColor

PlantHeight

PodShape

Round

Wrinkled

Round

Yellow

Green

Gray

White

Smooth

Constricted

Green

Yellow

Axial

Terminal

Tall

Short

Yellow Gray Smooth Green Axial Tall

Section 11-1

Figure 11-3 Mendel’s Seven F1 Crosseson Pea Plants

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Parental (P) Cross

•Mendel crossed two plants withcontrasting traits, a tall plant with ashort plant.•This initial pair is called the Parental(P) generation.•The offspring produced are calledthe First Filial (F1) generation.•The offspring of crosses betweenparents with different traits are calledhybrids.•The results of the cross produced alltall pea plants.

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F1 Cross• Mendel drew 2 conclusions from the results.

1. Biological inheritance is determined byfactors that are passed from onegeneration to the next.– These factors are genes.

2. Mendel’s principle of dominance whichstates that some alleles are dominantand others are recessive.

• Mendel wanted to find out if the short genedisappeared or was it hidden.

• Mendel self-pollinated the F1 generation toproduce a F2 generation.

• The results produced 3 tall plants for every 1short plant.

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P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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P Generation F1 Generation F2 Generation

Tall Short Tall TallTall Tall Tall Short

Section 11-1

Principles of Dominance

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Explanation of the F1 Cross•Mendel assumed the dominantallele masked the recessive allele.•The reappearance of the recessiveallele in the F2 generation indicatedthe allele for shortness separated, orsegregated, from the tall allele.•Mendel assumed this happenedduring the formation of the gametes.•The alleles segregate and eachgamete contains only one allele.

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Tossing Coins

If you toss a coin, what is the probability of getting heads? Tails? If youtoss a coin 10 times, how many heads and how many tails would youexpect to get? Working with a partner, have one person toss a cointen times while the other person tallies the results on a sheet of paper.Then, switch tasks to produce a separate tally of the second set of 10tosses.

Section 11-2

Interest Grabber

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1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do theresults of your tosses compare? How about the results of your partner’stosses? How close was each set of results to what was expected?

2. Add your results to those of your partner to produce a total of 20 tosses.Assuming that you expect 10 heads and 10 tails in 20 tosses, how closeare these results to what was expected?

3. If you compiled the results for the whole class, what results would youexpect?

4. How do the expected results differ from the observed results?

Section 11-2

Interest Grabber continued

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11–2 Probability and Punnett SquaresA. Genetics and ProbabilityB. Punnett SquaresC. Probability and SegregationD. Probabilities Predict Averages

Section 11-2

Section Outline

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Genetics and Probability•The likelihood that a particular event will occur iscalled probability.•Take a coin flip of example, what are the chances ofgetting heads?•Your chances are 1 in 2 flips or 1 : 2 or 50 percent.•What are your chances to get 3 heads in a row?

– 1/2 X 1/2 X 1/2 = 1/8•The way in which alleles segregate is completelyrandom.•The principle of probability can be used to predict theoutcomes of genetic crosses.

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Punnett Squares

•A diagram that can show the gene combinations from a genetic cross.•Organisms that have identicalalleles for a trait are called homozygous.•Organisms that have two different alleles for the same traitare heterozygous.•Physical characteristics are called phenotypes.•Genetic characteristics are called genotypes.•Dominant traits are represented by capital letters, whilerecessive traits are represented by lower case letters.

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Section 11-2

Tt X Tt Cross

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Section 11-2

Tt X Tt Cross

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Probabilities Predict Averages

•Probability can not predict the precise outcome of anindividual event.•However, they can predict the average outcome of a largeevent.•The same holds true for genetics.•The larger the number of offspring, the closer the resultingnumbers will get to the predicted values.

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Height in Humans

Height in pea plants is controlled by one of two alleles; the allele for a tallplant is the dominant allele, while the allele for a short plant is therecessive one. What about people? Are the factors that determine heightmore complicated in humans?

Section 11-3

Interest Grabber

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1. Make a list of 10 adults whom you know. Next to the name of eachadult, write his or her approximate height in feet and inches.

2. What can you observe about the heights of the ten people?

3. Do you think height in humans is controlled by 2 alleles, as it is in peaplants? Explain your answer.

Section 11-3

Interest Grabber continued

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11–3 Exploring Mendelian GeneticsA. Independent Assortment

1. The Two-Factor Cross: F1

2. The Two-Factor Cross: F2

B. A Summary of Mendel’s PrinciplesC. Beyond Dominant and Recessive Alleles

1. Incomplete Dominance2. Codominance3. Multiple Alleles4. Polygenic Traits

D. Applying Mendel’s PrinciplesE. Genetics and the Environment

Section 11-3

Section Outline

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Two Factor Crosses

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Section 11-3

Figure 11-10 Independent Assortment in Peas

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concludedthat

which iscalled the

which iscalled the

GregorMendel

Law ofDominance

Law ofSegregation

Peaplants

“Factors”determine

traitsSome alleles are dominant,

and some alleles are recessive

Alleles are separated during gamete formation

Section 11-3

Concept Map

experimentedwith

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Incomplete Dominance

•A scenario where neither gene is dominant over the other.•Example:

– Red snapdragon crossed with a white snapdragonproduces a pink snapdragon.

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Section 11-3

Figure 11-11 Incomplete Dominance inFour O’Clock Flowers

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Section 11-3

Figure 11-11 Incomplete Dominance inFour O’Clock Flowers

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Codominance

•A situation where both alleles contribute to the phenotype.•Example:

– Certain chickens with black feathers crossed with a chicken withwhite feathers produces an offspring with both black and whitefeathers.

X =

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Multiple Alleles•Genes that have more than two alleles for a gene.•Examples:

– Blood types in humans: A, B, AB, or O– Human hair or eye color– Fur color in rabbits

Full Color Chinchilla Himalayan Albino

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Polygenic Traits

•Traits that are controlled by two or more genes.•Example:

– Human skin colors

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How Many Chromosomes?

Normal human body cells each contain 46 chromosomes. The cell divisionprocess that body cells undergo is called mitosis and produces daughtercells that are virtually identical to the parent cell. Working with a partner,discuss and answer the questions that follow.

Section 11-4

Interest Grabber

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1. How many chromosomes would a sperm or an egg contain if either oneresulted from the process of mitosis?

2. If a sperm containing 46 chromosomes fused with an egg containing 46chromosomes, how many chromosomes would the resulting fertilizedegg contain? Do you think this would create any problems in thedeveloping embryo?

3. In order to produce a fertilized egg with the appropriate number ofchromosomes (46), how many chromosomes should each sperm andegg have?

Section 11-4

Interest Grabber continued

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11–4 MeiosisA. Chromosome NumberB. Phases of Meiosis

1. Meiosis I2. Meiosis II

C. Gamete FormationD. Comparing Mitosis and Meiosis

Section 11-4

Section Outline

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Section 11-4

Crossing-Over

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Section 11-4

Crossing-Over

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Section 11-4

Crossing-Over

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Meiosis I

Section 11-4

Figure 11-15 Meiosis

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Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

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Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

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Section 11-4

Figure 11-15 Meiosis

Meiosis I

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Section 11-4

Figure 11-15 Meiosis

Meiosis I

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Meiosis II

Meiosis I results in twohaploid (N) daughter cells,each with half the number ofchromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in asimilar way to the metaphasestage of mitosis.

The sister chromatidsseparate and move towardopposite ends of the cell.

Meiosis II results in fourhaploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Meiosis II

Meiosis I results in twohaploid (N) daughter cells,each with half the number ofchromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in asimilar way to the metaphasestage of mitosis.

The sister chromatidsseparate and move towardopposite ends of the cell.

Meiosis II results in fourhaploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Meiosis II

Meiosis I results in twohaploid (N) daughter cells,each with half the number ofchromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in asimilar way to the metaphasestage of mitosis.

The sister chromatidsseparate and move towardopposite ends of the cell.

Meiosis II results in fourhaploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Meiosis II

Meiosis I results in twohaploid (N) daughter cells,each with half the number ofchromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in asimilar way to the metaphasestage of mitosis.

The sister chromatidsseparate and move towardopposite ends of the cell.

Meiosis II results in fourhaploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Meiosis II

Meiosis I results in twohaploid (N) daughter cells,each with half the number ofchromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in asimilar way to the metaphasestage of mitosis.

The sister chromatidsseparate and move towardopposite ends of the cell.

Meiosis II results in fourhaploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

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Gamete Formation

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Forever Linked?

Some genes appear to be inherited together, or “linked.” If two genesare found on the same chromosome, does it mean they are linked forever?Study the diagram, which shows four genes labeled A–E and a–e, andthen answer the questions on the next slide.

Section 11-5

Interest Grabber

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1. In how many places can crossing over result in genes A and b being onthe same chromosome?

2. In how many places can crossing over result in genes A and c being onthe same chromosome? Genes A and e?

3. How does the distance between two genes on a chromosome affect thechances that crossing over will recombine those genes?

Section 11-5

Interest Grabber continued

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11–5 Linkage and Gene MapsA. Gene LinkageB. Gene Maps

Section 11-5

Section Outline

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Earth

Country

State

City

People

Cell

Chromosome

Chromosomefragment

Gene

Nucleotidebase pairs

Section 11-5

Comparative Scale of a Gene Map

Mapping ofEarth’s Features

Mapping of Cells,Chromosomes, and Genes

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Exact location on chromosomes Chromosome 2

Section 11-5

Figure 11-19 Gene Map of the Fruit Fly

Video Contents

Videos

Click a hyperlink to choose a video.Meiosis OverviewAnimal Cell Meiosis, Part 1Animal Cell Meiosis, Part 2Segregation of ChromosomesCrossing Over

Video 1

Click the image to play the video segment.

Video 1

Meiosis Overview

Video 2

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Video 2

Animal Cell Meiosis, Part 1

Video 3

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Video 3

Animal Cell Meiosis, Part 2

Video 4

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Video 4

Segregation of Chromosomes

Video 5

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Video 5

Crossing Over

Internet

The latest discoveries in geneticsInteractive test

Articles on genetics

For links on Punnett squares, go to www.SciLinks.org and enter theWeb Code as follows: cbn-4112.For links on Mendelian genetics, go to www.SciLinks.org and enterthe Web Code as follows: cbn-4113.For links on meiosis, go to www.SciLinks.org and enter the WebCode as follows: cbn-4114.

Go Online

Section 1 Answers

Interest Grabber Answers

1. In the first generation of each experiment, how do the characteristics of theoffspring compare to the parents’ characteristics?All offspring had the same characteristic, which was like one of theparents’. The other characteristic seemed to have disappeared.

2. How do the characteristics of the second generation compare to thecharacteristics of the first generation?Both characteristics appeared in this generation. The characteristic thathad “disappeared” in the first generation did not appear as often as theother characteristic. (It appears about 25 percent of the time.)

Section 2 Answers

Interest Grabber Answers

1. Assuming that you expect 5 heads and 5 tails in 10 tosses, how do theresults of your tosses compare? How about the results of your partner’stosses? How close was each set of results to what was expected?Results will vary, but should be close to 5 heads and 5 tails.

2. Add your results to those of your partner to produce a total of 20 tosses.Assuming that you expect 10 heads and 10 tails in 20 tosses, how close arethese results to what was expected?The results for 20 tosses may be closer to the predicted 10 heads and 10 tails.

3. If you compiled the results for the whole class, what results would you expect?The results for the entire class should be even closer to the number predictedby the rules of probability.

4. How do the expected results differ from the observed results?The observed results are usually slightly different from theexpected results.

Section 3 Answers

Interest Grabber Answers

1. Make a list of 10 adults whom you know. Next to the name of each adult,write his or her approximate height in feet and inches.Check students’ answers to make sure they are realistic.

2. What can you observe about the heights of the ten people?Students should notice that there is a range of heights in humans.

3. Do you think height in humans is controlled by 2 alleles, as it is in peaplants? Explain your answer.No, height does not seem to be controlled by two alleles, as it is in peaplants. Height in humans can vary greatly and is not just found in tall andshort phenotypes.

Section 4 Answers

Interest Grabber Answers

1. How many chromosomes would a sperm or an egg contain if either oneresulted from the process of mitosis?46 chromosomes

2. If a sperm containing 46 chromosomes fused with an egg containing 46chromosomes, how many chromosomes would the resulting fertilized eggcontain? Do you think this would create any problems in the developingembryo?46 + 46 = 92; a developing embryo would not survive if it contained 92chromosomes.

3. In order to produce a fertilized egg with the appropriate number ofchromosomes (46), how many chromosomes should each sperm and egghave?Sperm and egg should each have 23 chromosomes.

Section 5 Answers

Interest Grabber Answers

1. In how many places can crossing over result in genes A and b being on thesame chromosome?One (between A and B)

2. In how many places can crossing over result in genes A and c being on thesame chromosome? Genes A and e?Two (between A and B and A and C); Four (between A and B, A and C, Aand D, and A and E)

3. How does the distance between two genes on a chromosome affect thechances that crossing over will recombine those genes?The farther apart the genes are, the more likely they are to be recombinedthrough crossing over.

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