Question

question 1-8
one of the parents of a child has phenylketonuria (pku), which is caused by recessive alleles. the other parent does not have the pku alleles. what is the chance that the couple will have a child with phenylketonuria?
100 %
0%
50%
75%

Explanation:

Step1: Define allele notation

Let the recessive PKU allele be $a$, and the dominant non-PKU allele be $A$.

Step2: Identify parental genotypes

Parent with PKU (recessive disorder) must be $aa$. Parent without PKU alleles is $AA$.

Step3: Set up Punnett square

$$\begin{array}{c|cc} & A & A \\ \hline a & Aa & Aa \\ a & Aa & Aa \\ \end{array}$$

Step4: Calculate affected offspring chance

All offspring are $Aa$ (carriers, no PKU). So chance of affected child is 0%.

Answer:

0%