1. Steps to solving Punnett Squares

2. Example # 1
In a certain species of mouse, pointed ears are dominant over round ears.
Predict the genotypes and phenotypes of a cross between two hybrid pointed-eared mice.

3. Write a key. Include both alleles.
P= pointed ears
p= round ears

4. Write a “cross” to show the parents’ genotypes.
Parent one= Pp
Parent two= Pp

5. Write the parents’ genotypes (letters) around the outside of the square.
Parent One
P p P p
Parent Two

6. Fill in the square- copy letters down and across.
Parent One
P p P p PP
Parent Two Pp Pp pp

7. Write the percentage chance for the offspring’s genotypes
Parent One
P p P p
25%= PP (Homozygous Dominant)
50%= Pp (Heterozygous)
25%= pp (Homozygous Recessive) PP Pp
Parent Two pp Pp

8. Write the percentage chance for the offspring’s phenotypes
75% chance of having Pointed Ears

9. Try it yourself
In a certain species of dog, a black nose is dominant over a pink nose.
Predict the genotypes and phenotypes of a cross between a purebred dominant male dog and a purebred recessive female.

10. Here are the Steps: Write a key. Include both alleles.
Write a “cross” to show the parents’ genotypes.
Write the parents’ genotypes (letters) around the outside of the square.
Fill in the square- copy letters down and across.
Write the percentage chance for the offspring’s genotypes
Write the percentage chance for the offspring’s phenotypes