Question

homework - genetic tools
a man and a woman are both heterozygous for phenylketonuna (pku), an autosomal recessi
having children?
there is a 25% chance their children will have the disorder
there is a 50% chance their sons will have the disorder
there is a 50% chance their daughters will be carriers of the disorder
there is a 75% chance their children will have the disorder

Explanation:

Let the dominant allele be \(A\) and the recessive allele be \(a\). Both parents are heterozygous (\(Aa\)). Using a Punnett square:

Gametes of Father	Gametes of Mother
\(A\)	\(AA\)	\(Aa\)
\(a\)	\(Aa\)	\(aa\)

The genotypes of offspring are \(AA:Aa:aa = 1:2:1\). The probability of \(aa\) (having the disorder) is \(\frac{1}{4}=25\%\). Sons and daughters have the same probability as it is autosomal. The probability of being a carrier (\(Aa\)) is \(50\%\) for both sons and daughters.

Answer:

There is a 25% chance their children will have the disorder.