12.If nondisjunction of the sex chromosomes takes place in meiosis I in the male in Figure 4.5, what sexual phenotypes and proportions of offspring will be produced?

13.What will be the phenotypic sex of a human with the following genes or chromosomes or both?

*14.Joe has classic hemophilia, an X-linked recessive disease. Could Joe have inherited the gene for this disease from the following persons?

*15.In Drosophila, yellow body color is due to an X-linked gene that is recessive to the gene for gray body color.

16.Coat color in cats is determined by genes at several different loci. At one locus on the X chromosome, one allele (X⁺) encodes black fur; another allele (X^o) encodes orange fur. Females can be black (X⁺X⁺), orange (X^oX^o). or a mixture of orange and black called tortoiseshell (X⁺X^o). Males are either black (X⁺Y) or orange (X^oY), Bill has a female tortoiseshell cat named Patches. One night Patches escapes from Bill’s house, spends the night out, and mates with a stray male. Patches later gives birth to the following kittens: one orange male, one black male, two tortoiseshell females, and one orange female. Give the genotypes of Patches, her kittens, and the stray male with which Patches mated.

17.Red–green color blindness in humans is due to an X-linked recessive gene. Both John and Cathy have normal color vision. After 10 years of marriage to John, Cathy gave birth to a color-blind daughter. John filed for divorce, claiming that he is not the father of the child. Is John justified in his claim of nonpaternity? Explain why. If Cathy had given birth to a color-blind son, would John be justified in claiming nonpaternity?

18. The following pedigree illustrates the inheritance of Nance–Horan syndrome, a rare genetic condition in which affected persons have cataracts and abnormally shaped teeth.

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*19.Bob has XXY chromosomes (Klinefelter syndrome) and is color blind. His mother and father have normal color vision, but his maternal grandfather is color blind. Assume that Bob’s chromosome abnormality arose from nondisjunction in meiosis. In which parent and in which meiotic division did nondisjunction take place? Assume that no crossing over has taken place. Explain your answer.

20.The Talmud, an ancient book of Jewish civil and religious laws, states that if a woman bears two sons who die of bleeding after circumcision (removal of the foreskin from the penis), any additional sons that she has should not be circumcised. (The bleeding is most likely due to the X-linked disorder hemophilia.) Furthermore, the Talmud states that the sons of her sisters must not be circumcised, whereas the sons of her brothers should be. Is this religious law consistent with sound genetic principles? Explain your answer.

21. Craniofrontonasal syndrome (CFNS) is a birth defect in which premature fusion of the cranial sutures leads to abnormal head shape, widely spaced eyes, nasal clefts, and various other skeletal abnormalities. George Feldman and his colleagues looked at several families in which CFNS occurred and recorded the results shown in the following table (G. J. Feldman. 1997. Human Molecular Genetics 6:1937–1941).

22.How many Barr bodies would you expect to see in a human cell containing the following chromosomes?

23.What is the most likely sex and genotype of the cat shown in Figure 4.12?

24.Red–green color blindness is an X-linked recessive trait in humans. Polydactyly (extra fingers and toes) is an autosomal dominant trait. Martha has normal fingers and toes and normal color vision. Her mother is normal in all respects, but her father is color blind and polydactylous. Bill is color blind and polydactylous. His mother has normal color vision and normal fingers and toes. If Bill and Martha marry, what types and proportions of children can they produce?

*25.Miniature wings in Drosophila result from an X-linked gene (X^m) that is recessive to an allele for long wings (X⁺). Sepia eyes are produced by an autosomal gene (s) that is recessive to an allele for red eyes (s⁺).

*26.Palomino horses have a golden yellow coat, chestnut horses have a brown coat, and cremello horses have a coat that is almost white. A series of crosses between the three different types of horses produced the following offspring:

27.The L^M and L^N alleles at the MN blood group locus exhibit codominance. Give the expected genotypes and phenotypes and their ratios in progeny resulting from the following crosses.

*28.Assume that long earlobes in humans are an autosomal dominant trait that exhibits 30% penetrance. A person who is heterozygous for long earlobes mates with a person who is homozygous for normal earlobes. What is the probability that their first child will have long earlobes?

*29.When a Chinese hamster with white spots is crossed with another hamster that has no spots, approximately ½ of the offspring have white spots and ½ have no spots. When two hamsters with white spots are crossed, ²/₃ of the offspring possess white spots and ¹/₃ have no spots.

30. In the early 1900s, Lucien Cuénot, a French scientist working at the University of Nancy, studied the genetic basis of yellow coat color in mice. He carried out a number of crosses between two yellow mice and obtained what he thought was a 3 : 1 ratio of yellow to gray mice in the progeny. The following table gives Cuénot’s actual results, along with the results of a much larger series of crosses carried out by William Castle and Clarence Little (W. E. Castle and C. C. Little. 1910. Science 32:868–870).

31.In rabbits, an allelic series helps to determine coat color: C (full color), c^ch (chinchilla, gray color), c^h (Himalayan, white with black extremities), and c (albino, all white). The C allele is dominant over all others, c^ch is dominant over c^h and c, c^h is dominant over c, and c is recessive to all the other alleles. This dominance hierarchy can be summarized as C > c^ch > c^h > c. The rabbits in the list below are crossed and produce the progeny shown. Give the genotypes of the parents for each cross.

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*32.In this chapter, we considered Joan Barry’s paternity suit against Charlie Chaplin and how, on the basis of blood types, Chaplin could not have been the father of her child.

*33.In chickens, comb shape is determined by alleles at two loci (R, r and P, p). A walnut comb is produced when at least one dominant allele R is present at one locus and at least one dominant allele P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive alleles are present at the first locus and at least one dominant allele is present at the second (genotype rr P_). If two recessive alleles are present at the first locus and at the second locus (rr pp), a single comb is produced. Progeny with what types of combs and in what proportions will result from the following crosses?

34. Tatuo Aida investigated the genetic basis of color variation in the medaka (Aplocheilus latipes), a small fish found in Japan (T. Aida. 1921. Genetics 6:554–573). Aida found that genes at two loci (B, b and R, r) determine the color of the fish: fish with a dominant allele at both loci (B_ R_) are brown, fish with a dominant allele at the B locus only (B_ rr) are blue, fish with a dominant allele at the R locus only (bb R_) are red, and fish with recessive alleles at both loci (bb rr) are white. Aida crossed a homozygous brown fish with a homozygous white fish. He then backcrossed the F₁ with the homozygous white parent and obtained 228 brown fish, 230 blue fish, 237 red fish, and 222 white fish.

35. E. W. Lindstrom crossed two corn plants with green seedlings and obtained the following progeny: 3583 green seedlings, 853 virescent-white seedlings, and 260 yellow seedlings (E. W. Lindstrom. 1921. Genetics 6:91–110).

*36.A summer-squash plant that produces disc-shaped fruit is crossed with a summer-squash plant that produces long fruit. All the F₁ have disc-shaped fruit. When the F₁ are intercrossed, F₂ progeny are produced in the following ratio: ⁹/₁₆ disc-shaped fruit; ⁶/₁₆ spherical fruit; ¹/₁₆ long fruit. Give the genotypes of the F₂ progeny.

37.Some sweet-pea plants have purple flowers and others have white flowers. A homozygous variety of sweet pea that has purple flowers is crossed with a homozygous variety that has white flowers. All the F₁ have purple flowers. When these F₁ are self-fertilized, the F₂ appear in a ratio of ⁹/₁₆ purple to ⁷/₁₆ white.

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*38.The direction of shell coiling in the snail Lymnaea peregra (discussed in the introduction to this chapter) results from a genetic maternal effect. An autosomal allele for a right-handed shell (s⁺), called dextral, is dominant over the allele for a left-handed shell (s), called sinistral. A pet snail called Martha is sinistral and reproduces only as a female (the snails are hermaphroditic). Indicate which of the following statements are true and which are false. Explain your reasoning in each case.

39.If the F₂ dextral snails with genotype S⁺s in Figure 4.21 undergo self-fertilization, what phenotypes and proportions are expected to occur in the progeny?

40.Which of the following statements is an example of a phenocopy? Explain your reasoning.

41.Match each of the following terms with its correct definition (parts a through h).