Download Sex-Linked Problems

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?