GENETICS PROBLEMS
You WILL see at LEAST 1-2 of these genetics problems on your final exam. It may be beneficial for you
to work through these problems before your last exam. For each of these problems, be sure to justify
your answer(s) by including an allele key, parental cross (genotypes), phenotypes, and the resulting
Punnett square representing all possible matings of eggs and sperm.
1. Aura and Ryan are expecting a child. Aura has dark eyes and Ryan has light eyes. Is there any way
their child could have light eyes, even if light is recessive to dark? Hint: Aura’s mother had light
eyes. Justify using Punnett squares.
2. Tom and his wife Julie are both carriers for cystic fibrosis, an autosomal recessive disease. What is
the chance that their first child will have cystic fibrosis? Is a carrier?
3. In cattle, a dominant “Dexter” gene, combined with its recessive allele, results in abnormally short
legs, while the homozygous dominant condition results in such severe deformities that the fetal calf
nearly always dies in utero. If a cow and bull, each heterozygous for the Dexter gene, are mated,
what is the chance that they will produce a calf with normal legs?
4. Denise has light hair and dark eyes, while Jon has dark hair and dark eyes. The genes for these
traits assort independently. Denise is homozygous for hair color, but heterozygous for eye color. Jon
is heterozygous for both. Dark eyes are dominant to blue eyes, and dark hair is dominant to blond
hair. Determine the expected genotypes and phenotypes of Denise and Jon’s children, and
additionally state the probability the couple will have a dark haired, blue-eyed child?
5. In guinea pigs, the short hair allele (H) shows complete dominance to the long hair allele (h). Hair
color, on the other hand, is a partial dominant trait in which the heterozygote (CC’) has cream-colored
hair, while the homozygotes have either white hair (CC), or yellow hair (C’C’). If a yellow, long-haired
guinea pig is mated with a white, homozygous short-haired guinea pig, what would be the expected
genotypes and phenotypes of the F1 generation and in what proportion?
6. In general, what percentage of human offspring would be expected to receive:
(a.) an X chromosome from their mother?
(b.) an X chromosome from their father?
(c.) a Y chromosome from their father?
Explain each of your answers above briefly
7. The Martin family knows of three relatives who had kinky hair disease, a sex-linked recessive
disorder in which a child does not grow, experiences brain degeneration, and dies by the age of two
years. Affected children have peculiar white stubby hair, from which the disorder takes its name.
Joan Martin is hesitant about having children because her two sisters have each had sons who died
from kinky hair disease.
(a.) If Joan is a carrier, what is the chance that a son of hers would inherit kinky hair disease?
(b.) Explain why none of the women in the family have kinky hair disease.
8. “Hairy ears” is an unusual, sex-linked Y-linked trait. If Kyle, with hairy ears, marries Heather, with
normal ears, what are the expected genotypes and phenotypes of their children? What is the
probability the Kyle and Heather will have hairy-eared daughters? Hairy eared sons?
9. Dina has not been very careful and does not know which of her “friends” is the father of her child.
Dina has Type A blood, and her baby is Type B. The father is one of three men: Charlie, who is
Type O, Joe, who is Type A, and Al, who is Type AB. Which one is the father?