Phenylketonuria is an inherited disease caused by a recessive autosomal allele. if a woman and her husband are both carriers, what is the probability that their first child will be a phenotypically normal girl?

3/8

Explanation:

Given that both the parents are carrier for phenylketonuria, the genotype of both parent is "Aa".

Probability of getting phenotypically healthy child = Aa x Aa = 3/4 Healthy (1/2 AA and 1/2 Aa) : 1/4 affected (aa).

Probability of getting a girl child = XY x XX = 1/2 girl (XX) : 1/2 boy (XY).

Hence, probability that their first child will be a phenotypically normal girl = 3/4 healthy x 1/2 girl = 3/8 healthy girl child.

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