Punnett Square Practice Sheet - Show all work on a separate sheet of paper. Be neat!
1. Write the five steps to follow when completing a Punnett square.
2. Complete a Punnett square (monohybrid cross) with following genotypes.
Male-Yy
Female-yy
a. What is the phenotypic ratio?
b. What is the genotypic ratio?
3. Let Y=yellow flowers
y= purple flowers
a. What is the genotype for a homozygous yellow flower?
b. What is the genotype for a purple flower?
c. What is the genotype for a heterozygous yellow flower?
d. What is the genotype for a yellow flower that produced purple offspring?
4. Cross a heterozygous yellow flower with a purple flower.
a. What is the phenotypic ratio?
b. What is the genotypic ratio?
5. Albinism is a recessive condition in which the affected organism is unable to manufacture pigment. This causes
white hair and pink eyes. Cross two heterozygous individuals.
a. What is the phenotypic ratio?
b. What is the genotypic ratio?
c. Can these parents have albino children?
6. In humans unattached ear lobes are dominant to attached ear lobes.
E= unattached
e=attached
If your mother has attached ear lobes, you have attached ear lobes and your brother has unattached ear lobes.
What is the phenotype of your father?
2 Factor Crosses - Show all work on a separate sheet of paper. Be neat!
7. In a certain type of hamster, tan color (T) is completely dominate over brown and a curly coat (C) is completely
dominant over a smooth coat.
A. Identify the 2 traits and their corresponding alleles on your paper (include letters for each allele).
B. Write down the P cross and the F1 genotypes & phenotypes if a homozygous tan, smooth hamster is bred
to a brown homozygous curly hamster.
8. Some dogs bark when trailing, others are silent. The barking trait is believed to be due to a dominant gene (B),
silence to the recessive gene. Erect ears (E) are dominant over drooping ears. What kind of pups would be
expected from a heterozygous erect-eared, heterozygous barker mated to a droop-eared, silent trailer?
A. Write the P1 cross using the correct letters.
B. Genotypes & phenotypes of F1 generation?
9. A completely homozygous green (G) frog with spotted skin (S) mates with a female that is a green hybrid
carrying the recessive gene for cream color (g) and has a plain coat (no spots).
A. Write the different gametes produced by the male & female frog.
B. Write the P1 cross.
C. Give the genotypes and phenotypes for the F1 generation.