Transcript Steps to solving Punnett Squares

Steps to solving Punnett
Squares
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.

Write a key. Include both alleles.
P= pointed ears
 p= round ears

Write a “cross” to show the parents’
genotypes.
Parent one= Pp
 Parent two= Pp

Write the parents’ genotypes
(letters) around the outside of the
square.
Parent One
P
Parent Two
P
p
p
Fill in the square- copy letters down
and across.
Parent One
P
Parent Two
P
p
PP
Pp
Pp
p
pp
Write the percentage chance for the
offspring’s genotypes
Parent One
P
Parent Two
P
PP
p
Pp
25%= PP
(Homozygous
Dominant)
50%= Pp
(Heterozygous)
p
Pp
pp
25%= pp (Homozygous
Recessive)
Write the percentage chance for the
offspring’s phenotypes
75% chance of having Pointed Ears
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.

Here are the Steps:
1.
2.
3.
4.
5.
6.
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