Determining Genetic Risk

Using a Punnett Square

A Punnett Square can help determine the probability that offspring will have a particular phenotype or genotype.

Example: The possible offspring outcomes for parents who are both carriers of a cystic fibrosis mutation.

C- normal allele

c- allele with CF mutation

In this example, each child would have:

25% chance of being unaffected with Cystic Fibrosis (CC)

50% chance of being a carrier of Cystic Fibrosis (Cc)

25% chance of being affected with Cystic Fibrosis (cc)