Question A couple are both heterozygous for the autosomal re

Question A couple are both heterozygous for the autosomal recessive disease cystic fibrosis (CF). What is the probability that their first child will either be a boy or have CF? Answer Ao 3/8

Solution

1. Answer is 1/8.

Probability for boy = 1/2 and probability for cystic fibrosis = 1/4. Then probability either boy or have Cystic fibrosis = 1/2 x 1/4 = 1/8. It is based on multiplicative law.

2. Answer is 9/16. It is nased on additive law. Each time the probability of lacking Cystic fibrosis is 3/4.

3/4 + 3/4 = 9/16