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End Show Slide 1 of 18 Copyright Pearson Prentice Hall Biology.

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1 End Show Slide 1 of 18 Copyright Pearson Prentice Hall Biology

2 End Show Slide 2 of 18 Copyright Pearson Prentice Hall 11-5 Linkage and Gene Maps

3 End Show 11-5 Linkage and Gene Maps Slide 3 of 18 Copyright Pearson Prentice Hall Gene Linkage What structures actually assort independently?

4 End Show 11-5 Linkage and Gene Maps Slide 4 of 18 Copyright Pearson Prentice Hall Gene Linkage Thomas Hunt Morgan’s research on fruit flies led him to the principle of linkage. Morgan discovered that many of the more than 50 Drosophila genes he had identified appeared to be “linked” together. They seemed to violate the principle of independent assortment.

5 End Show 11-5 Linkage and Gene Maps Slide 5 of 18 Copyright Pearson Prentice Hall Morgan and his associates grouped the linked genes into four linkage groups. Each linkage group assorted independently but all the genes in one group were inherited together. Each chromosome is actually a group of linked genes. Gene Linkage

6 End Show 11-5 Linkage and Gene Maps Slide 6 of 18 Copyright Pearson Prentice Hall Gene Linkage Morgan concluded that Mendel’s principle of independent assortment still holds true. Chromosomes assort independently, not individual genes.

7 End Show 11-5 Linkage and Gene Maps Slide 7 of 18 Copyright Pearson Prentice Hall Gene Maps Crossing-over during meiosis sometimes separates genes that had been on the same chromosomes onto homologous chromosomes. Crossover events occasionally separate and exchange linked genes and produce new combinations of alleles.

8 End Show 11-5 Linkage and Gene Maps Slide 8 of 18 Copyright Pearson Prentice Hall Alfred Sturtevant, a student of Morgan, reasoned that the farther apart two genes were, the more likely they were to be separated by a crossover in meiosis. Recombination frequencies can be used to determine the distance between genes. Gene Maps

9 End Show 11-5 Linkage and Gene Maps Slide 9 of 18 Copyright Pearson Prentice Hall Sturtevant created a gene map showing the relative locations of each known gene on one of the Drosophila chromosomes. Gene Maps

10 End Show 11-5 Linkage and Gene Maps Slide 10 of 18 Copyright Pearson Prentice Hall If two genes are close together, the recombination frequency between them should be low, since crossovers are rare. If they are far apart, recombination rates between them should be high. Gene Maps

11 End Show 11-5 Linkage and Gene Maps Slide 11 of 18 Copyright Pearson Prentice Hall Gene Maps Aristaless (no bristles on antenna) Chromosome 2Exact location on chromosome 13.0 Dumpy wing Black body 54.5 Purple eye 67.0 Vestigial (small) wing 99.2 Arc (bent wings) Speck wing

12 End Show 11-5 Linkage and Gene Maps Slide 12 of 18 Copyright Pearson Prentice Hall Chromosome 2Exact location on chromosome 1.3 Star eye 31.0 Dachs (short legs) 51.0 Reduced bristles 55.0Light eye 75.5 Curved wing Brown eye Gene Maps

13 End Show - or - Continue to: Click to Launch: Slide 13 of 18 Copyright Pearson Prentice Hall 11-5

14 End Show Slide 14 of 18 Copyright Pearson Prentice Hall 11-5 According to Mendel's principle of independent assortment, the factors that assort independently are the a.genes. b.chromosomes. c.chromatids. d.gametes.

15 End Show Slide 15 of 18 Copyright Pearson Prentice Hall 11-5 A chromosome is actually a group of a.independent genes. b.linkage groups. c.crossed-over genes. d.linked genes.

16 End Show Slide 16 of 18 Copyright Pearson Prentice Hall 11-5 Thomas H. Morgan is credited with the discovery of the principle of a.segregation. b.independent assortment. c.gene linkage. d.dominance.

17 End Show Slide 17 of 18 Copyright Pearson Prentice Hall 11-5 Linkage maps can be produced because the farther apart two genes are on a chromosome, a.the less likely they are to assort independently. b.the more likely they are to be linked. c.the more likely they are to be separated by a crossover. d.the less likely they are to be separated by a crossover.

18 End Show Slide 18 of 18 Copyright Pearson Prentice Hall 11-5 If two genes are close together on the same chromosome, they are more likely to a.behave as though they are linked. b.behave independently. c.move to different chromosomes. d.belong to different linkage groups.

19 End Show Slide 19 of 18 Copyright Pearson Prentice Hall 11-2 Probability and Punnett Squares

20 End Show Slide 20 of 18 Copyright Pearson Prentice Hall How do geneticists use the principles of probability? Genetics and Probability

21 End Show Slide 21 of 18 Copyright Pearson Prentice Hall Genetics and Probability The likelihood that a particular event will occur is called probability. The principles of probability can be used to predict the outcomes of genetic crosses.

22 End Show Slide 22 of 18 Copyright Pearson Prentice Hall Punnett Squares How do geneticists use Punnett squares?

23 End Show Slide 23 of 18 Copyright Pearson Prentice Hall Punnett Squares The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

24 End Show Slide 24 of 18 Copyright Pearson Prentice Hall A capital letter represents the dominant allele for tall. A lowercase letter represents the recessive allele for short. In this example, T = tall t = short Punnett Squares

25 End Show Slide 25 of 18 Copyright Pearson Prentice Hall Gametes produced by each F 1 parent are shown along the top and left side. Punnett Squares

26 End Show Slide 26 of 18 Copyright Pearson Prentice Hall Punnett Squares Possible gene combinations for the F 2 offspring appear in the four boxes.

27 End Show Slide 27 of 18 Copyright Pearson Prentice Hall Punnett Squares Organisms that have two identical alleles for a particular trait are said to be homozygous. Organisms that have two different alleles for the same trait are heterozygous. Homozygous organisms are true-breeding for a particular trait. Heterozygous organisms are hybrid for a particular trait.

28 End Show Slide 28 of 18 Copyright Pearson Prentice Hall Punnett Squares All of the tall plants have the same phenotype, or physical characteristics. The tall plants do not have the same genotype, or genetic makeup. One third of the tall plants are TT, while two thirds of the tall plants are Tt.

29 End Show Slide 29 of 18 Copyright Pearson Prentice Hall Punnett Squares a.The plants have different genotypes (TT and Tt), but they have the same phenotype (tall). TT Homozygous Tt Heterozygous

30 End Show Slide 30 of 18 Copyright Pearson Prentice Hall Probability and Segregation a.One fourth (1/4) of the F 2 plants have two alleles for tallness (TT). b.2/4 or 1/2 have one allele for tall (T), and one for short (t). c.One fourth (1/4) of the F 2 have two alleles for short (tt).

31 End Show Slide 31 of 18 Copyright Pearson Prentice Hall Probability and Segregation Because the allele for tallness (T) is dominant over the allele for shortness (t), 3/4 of the F 2 plants should be tall. The ratio of tall plants (TT or Tt) to short (tt) plants is 3:1. The predicted ratio showed up in Mendel’s experiments indicating that segregation did occur.

32 End Show Slide 32 of 18 Copyright Pearson Prentice Hall Probabilities Predict Averages a.Probabilities predict the average outcome of a large number of events. b.Probability cannot predict the precise outcome of an individual event. c.In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

33 End Show Slide 33 of 18 Copyright Pearson Prentice Hall 11-2

34 End Show Slide 34 of 18 Copyright Pearson Prentice Hall 11-2 Probability can be used to predict a.average outcome of many events. b.precise outcome of any event. c.how many offspring a cross will produce. d.which organisms will mate with each other.

35 End Show Slide 35 of 18 Copyright Pearson Prentice Hall 11-2 Compared to 4 flips of a coin, 400 flips of the coin is a.more likely to produce about 50% heads and 50% tails. b.less likely to produce about 50% heads and 50% tails. c.guaranteed to produce exactly 50% heads and 50% tails. d.equally likely to produce about 50% heads and 50% tails.

36 End Show Slide 36 of 18 Copyright Pearson Prentice Hall 11-2 Organisms that have two different alleles for a particular trait are said to be a.hybrid. b.heterozygous. c.homozygous. d.recessive.

37 End Show Slide 37 of 18 Copyright Pearson Prentice Hall 11-2 Two F 1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? a.100% b.50% c.0% d.25%

38 End Show Slide 38 of 18 Copyright Pearson Prentice Hall 11-2 The Punnett square allows you to predict a.only the phenotypes of the offspring from a cross. b.only the genotypes of the offspring from a cross. c.both the genotypes and the phenotypes from a cross. d.neither the genotypes nor the phenotypes from a cross.


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