Punnett Square Practice Problems
1. Webbed fingers is inherited as an X-linked disease. An unaffected male marries an
affected female.
a. Draw a Punnett square of the possible offspring.
b. List the phenotypes of the possible children.
c. Draw a pedigree that displays the inheritance in your Punnett Square.
d. One of the boys marries. They have two children. The boy is unaffected. The
girl is a carrier. What is the genotype of their mom? (Add this to your pedigree
in ‘C’.
2. Colorblindness is inherited as a sex-linked recessive disease. An affected male marries a
heterozygous female.
a. Draw a Punnett square of the possible offspring.
b. List the phenotypes of the possible children.
c. Draw a pedigree that displays the inheritance in your Punnett Square.
d. If the heterozygous daughter marries an unaffected male, can you predict the
offspring? If so, add the information to your pedigree. If not, explain why.
3. Hairy ears is inherited as a Y-linked trait. A man with hairy ears marries a woman with
normal ears.
a. Draw a Punnett square of the possible offspring.
b. Could any of their children have hairy ears?
c. Draw a pedigree that displays the inheritance in your Punnett Square.
d. Can this trait be ‘bred out’ of the family line? If so, how? If not, why?
4. In dogs, deafness is inherited as an autosomal recessive gene. A kennel owner has a male
dog that she wants to use for breeding purposes if possible. The dog can hear, but the
owner wants to be sure he is not a carrier of the recessive gene.
a. Draw the Punnett square(s) needed to illustrate the possible crosses.
b. In each case, what percentage/how many of the offspring would be expected to be
able to hear? To be deaf?
c. If the male dog is heterozygous for deafness, can this trait be ‘bred out’ of the
family line? If so, how? If not, why?
5. Baldness is inherited as sex-linked dominant disease. An affected male marries a
homozygous recessive female.
a. Draw a Punnett square of the possible offspring.
b. List the phenotypes of the possible children.
c. Draw a pedigree that displays the inheritance in your Punnett Square.
d. What were the genotypes of both sets of grandparents? Add this information to
your pedigree.