This document provides 9 practice problems involving Punnett squares. Each problem describes a genetic cross between organisms and asks the reader to: 1) state the genotypes of the parents involved in the cross, 2) draw and complete a Punnett square showing the possible genotypes of the offspring, and 3) state the phenotypic ratios expected among the offspring. The problems cover genetic crosses involving traits such as whisker length in seals, horn presence in mythical creatures, flower color and seed coat traits in peas, eye color in humans, ear shape in dogs, and toe curling in humans.

1. Punnett Square
Practice Problems

2.  1. Let’s say that in seals, the gene for the
length of the whiskers has two alleles. The
dominant allele (W) codes long whiskers &
the recessive allele (w) codes for short
whiskers.
◦ A. What percentage of offspring would be expected to
have short whiskers from the cross of two long
whiskered seals, one parent is purebred dominant and
the other one is hybrid?
◦ B. If one parent seal is pure long whiskered and the
other is short whiskered, what percent of offspring would
have short whiskers?

3.  2. In purple people eaters, one horn is
dominant and no horn is recessive.
◦ A. Draw a Punnett Square showing the cross of
a purple people eater that is hybrid for horns
with a purple people eater that does not have
horns.
◦ B. Summarize the genotype & phenotypes of
the possible offspring.

4.  3. A green-leafed fuzzywhatsit (I made
this plant up) is crossed with a
fuzzywhatsit with yellow-striped leaves.
The cross produces 4 green-leafed
fuzzywhatsits.
◦ A. What were the genotype of both parents?
◦ B. Summarize the genotypes & phenotypes of
the offspring produced.

5.  4. In dogs, there is a hereditary deafness
caused by a recessive gene, “d”. A kennel
owner has a male dog that she wants to use
for breeding purposes if possible. The dog
can hear, so the owner knows his genotype is
either DD or Dd. If the dog’s genotype is Dd,
the owner does not wish to use him for
breeding so that the deafness gene will not
be passed on. This can be tested by breeding
the dog to a deaf female (dd).
◦ A. Draw the Punnett Square to illustrate the cross
between Dd and dd. What percent of the offspring
would be expected to be hearing? Deaf?
◦ B. Draw the Punnett Square to illustrate the cross
between DD and dd. What percent of the offspring
would be expected to be hearing? Deaf?
◦ C. Which gentype should the kennel owner be
hoping for? Why?

6.  5. In humans, brown eyes (B) are
dominant over blue (b). A brown-eyed
man marries a blue-eyed woman and they
have three children, two of whom are
brown-eyed and one of whom is blue-
eyed.
◦ A. Draw the Punnett Square that illustrates this
marriage.
◦ B. What is the man’s genotype?
◦ C. What are the genotypes of the children?

7.  6. In garden peas, round seed coats (R) is
dominant over wrinkled seed coats (r).
What will the result be of a cross between
a purebred dominant male and a purebred
recessive female?
◦ A. List the genotypes of the parents.
◦ B. Diagram and complete a Punnett Square
◦ C. Give the phenotype percentages of the
offspring.

8.  7. In peas, yellow color (Y) is dominant to
green (y). What will be the results of a
cross-pollination of a hybrid female and a
hybrid male?
◦ A. List the genotypes of the parents.
◦ B. Diagram and complete a Punnett Square
◦ C. Give the phenotype percentages of the
offspring.

9.  8. In humans, straight toes (S) are
dominant over curled toes (s). What
would be the result of a cross between a
recessive male and a purebred dominant
female?
◦ A. List the genotypes of the parents.
◦ B. Diagram and complete a Punnett Square
◦ C. Give the phenotype percentages of the
offspring.

10.  9. In dogs, erect ears (E) are dominant
over droopy ears (e). What are the results
if two purebred recessive dogs have a
litter of puppies?
◦ A. List the genotypes of the parents.
◦ B. Diagram and complete a Punnett Square
◦ C. Give the phenotype percentages of the
offspring.