Question

A couple has four children. One child has phenylketonuria (PKU). What is the probability of occurrence of PKU in the second generation?

• A. 0
• B. 0.25
• C. 0.5
• D. 0.75
• E. 1

Answer 1

Answer: (B)

0.25

Phenylketonuria (PKU) is an autosomal recessive disease caused by a recessive allele p.

The child has PKU, i.e. his genotype would be pp. This means the child has acquired the p allele from both the parents and thus, the parents are heterozygous for this p allele i.e. they are carriers with genotype Pp.

The probability of occurrence of PKU in the second generation can be estimated from the cross as shown in the figure.

Hence, the probability of child with PKU in the second generation will be = 1/4= 0.25

So, the correct answer is '0.25'.