Question

Phenylketonuria, PKU, is a single-gene recessive human

diseaseresulting from an inability to break down phenylalanine.
Twounaffected (non-PKU) parents already have a child with PKU.
What's the probability that their next child will carry just
1recessive allele?

Answer 1

1/2

Step-by-step explanation:

Let's assume that the allele "p" is responsible for PKU in the homozygous state. According to the given information, both the parents are unaffected by the disorder but have an affected child. This means that both the parents carry at least one copy of the recessive allele responsible for the disease. Therefore, the genotype of each of the parents is Pp. A cross between Pp and Pp would produce progeny in following ratio=

Pp x Pp = 1/4 PP: 1/2/ Pp: 1/4 pp

Therefore, the probability that their next child will carry just one recessive allele is 1/2.