Punnet Square Practice Sheet
1. Create a punnet square for each of the following, then state the genotypes and
phenotypes.
a) Two heterozygous tall plants are crossed. The gene for tall (T) is dominant
over the gene for dwarf (t)
b) A heterozygous tall plant is crossed with a dwarf plant.
c) A plant that is homozygous for green pods is crossed with one that has
yellow pods. Green (G) is dominant over yellow (g).
d) A plant that is homozygous for round seeds is crossed with a plant that is
heterozygous for round seeds. Round (R) is dominant over wrinkled (r).
2. For Labrador retrievers, black fur colour is dominant over yellow.
a) What would be the genotype of a homozygous black dog? A heterozygous
black dog? (Pick appropriate letters for the genotypes).
b) Could the heterozygous black dog have the same genotype as a dog with
yellow fur? Why or why not?
3. A pea plant with round seeds is cross pollinated with a pea plant that has wrinkled
seeds.
a) What are the genotypes of the parents if the round-seed plant is
heterozygous?
b) What are the genotypes and phenotypes of the offspring? (Use a punnet
square to do this).
4. For Dalmatians, the spotted condition (S) is dominant over non-spotted (s).
a) Use a punnet square to show the results of a cross between two
heterozygous parents.
b) A spotted female Dalmatian mates with an unknown male. Half of the
pups have spots, and half do not. What are the genotypes and phenotypes
of the parents?