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Sex-Linked Problems 1. Hemophilia is a recessive sex-linked disorder. A man with hemophilia has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all four will be born with hemophilia. 2. A hemophiliac man marries a carrier woman. What is the probability that they have a child that is either a boy or a girl? What is the probability that they have a child who is a hemophiliac? What is the probability that they have a child who is a hemophiliac and a boy? 3. Muscular dystrophy is a sex-linked recessive disorder. A man with muscular dystrophy marries a woman who does not have this disease. Half of their daughters and half of their sons develop this disease. What is the genotype of the father? The mother? 4. Red-green color blindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was color blind. What is the probability that they will have a color-blind daughter? A son? 5. In cats, short hair is dominant over long hair; the gene involved is autosomal. Another gene B1, which is sex-linked, produces yellow coat color; its allele, B2, produces black coat color; and the heterozygous condition B1B2 produces tortoise-shell color. If a long-haired black male is mated with a tortoise-shell female homozygous for short hair, what kind of kittens will be produced in the F1 (genotype and phenotype)? 6. A man and his wife both have normal color vision, but a daughter has redgreen color blindness, a sex-linked recessive trait. The man sues his wife for divorce on grounds of infidelity. Can genetics provide evidence supporting his case? 7. In cats, a gene for coat color is sex-linked. Cats homozygous for allele A have yellow coats; those homozygous for allele a have black coats; and heterozygotes have tortoiseshell coats. What type(s) of offspring would result from a mating of a black male and a tortoise-shell female? Is it possible to obtain a tortoise-shell male? 8. Red-green color blindness is inherited as a sex-linked recessive. If a colorblind woman marries a man who has normal vision, what would be the expected phenotypes of their children with reference to this character? 9. On the X chromosome of Drosophila there may occur a recessive gene l, which is lethal in the larval stage. A heterozygous female is crossed to a normal male; what F1 adult sex phenotypic ratio results?