Download Punnett Square Worksheet 1

Name: _____________________________________________ Date: __________ Period: ______
Punnett Square Practice (pg. 36)
Directions: Read each problem carefully. Place the parent genotypes on the Punnett square. Fill in the Punnett
square. Calculate the probabilities for the offspring genotypes and phenotypes.
You need to know the definitions to the following terms, in order to complete this practice:
Dominant, Recessive, Genotype, Phenotype, Homozygous, Heterozygous, Hybrid, Purebred
1. Widow’s peaks are dominant over straight hairlines. Show the cross of one parent who has a BB
genotype for widow’s peak, and another parent who has a bb genotype and no widow’s peak.
You’ll
need to
make this
on your
own, for
the others.
BB =
Bb =
bb =
Widow’s peak =
Straight hairline =
2. In humans, brown hair is the dominant phenotype over the blonde hair phenotype. Show the cross of a
two parents that have a Bb genotype for hair color.
3. Blue eyes are the recessive phenotype, and brown eyes are the dominant phenotype, in humans. One
blue-eyed parent reproduces with a brown-eyed parent with the Bb genotype. Show the cross.
4. Most people in these two parents’ families have widow’s peaks, but each parent has some blood
relatives with straight hairlines. This means the parents probably have heterozygous genotypes for
widow’s peak. Show the cross.
5. One parent has the homozygous dominant genotype for eye color, with brown eyes. The other parent is
homozygous recessive, with blue eyes. Show the cross.
6. Two parents have the straight hairline phenotype. Show the cross of these two homozygous recessive
parents.
7. Challenge:
Part 1: One parent has brown eyes, and the other parent has blue eyes. Show both possible crosses.
Part 2: If they had a child with blue eyes, which cross would be accurate? Circle the Punnett square.
8. Dogs and humans’ genes for eye color work the same way: brown is dominant, and blue is recessive.
Show the cross of two purebred blue-eyed dogs.
9. Show the cross of a purebred blue-eyed dog, with a dog that is hybrid for eye color.
10. Show the cross of a purebred blue-eyed dog with a dog that is homozygous dominant for eye color.
Below, summarize the techniques & knowledge that were needed to complete these problems.