Question

at is the probability that their first child will be a phenotypically normal girl? 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?
A. 3/8
B. 1/4
C. 1/16
D. 3/16

Answer 1

Answer:

The ans will be $\frac{3}{8}$

Explanation:

As phenylketonuria is a recessive autosomal disease, and both the parents are carrier, so they both carry one defective gene and one good gene.

If they produced 4 children, the probability of diseased and non diseased child will be as follows.

diseased: $\frac{1}{4}$

non diseased:  $\frac{3}{4}$

And the probability of male and female child will be $\frac{1}{2}$.

So, the probability of phenotypically normal first girl child will be $\frac{3}{4}$ × $\frac{1}{2}$ ⇒ $\frac{3}{8}$