Punnet Square Notes

Punnett Square—table used to predict the characteristics of offspring from 2 parents

Example (to left) cross father who is heterozygous dominant (Bb) for brown hair, with mother who is homozygous recessive (bb) for blonde hair.

To make a Punnett Square:

• Take the alleles from one parent, and place one at the top of each column

 

• Take the alleles from the second parent, and place one on the left side of each row

 

• Copy the alleles from the top into each box below

 

• Copy each allele on the left into the boxes to the right

 

**If a dominant allele is present, the dominant trait will be expressed

**Only offspring that are homozygous recessive (2 recessive alleles) will express the recessive trait