Cystic fibrosis is an autosomal recessive disorder that affe

Cystic fibrosis is an autosomal recessive disorder that affects lung function in humans. A man and a woman are both unaffected heterozygous carriers of a cystic fibrosis gene. If the couple has two children, what is the probability that their first child will be unaffected and their second child will be unaffected? a) 6.25% b) 18.75% c) 37.5% d? 56.25%

Solution

Answer:

Chances of first child being unaffected = ¾

Chances of second child being unaffected = ¾

¾ x ¾ = 9/16 = 56.25%

Explanation:

In autosomal recessive inheritance, two copies of a disease allele are required for an individual to be susceptible to expressing the phenotype.

There is a one in four (25%) chance the offspring will inherit two copies of the disease allele and will therefore have the phenotype.