What is the probability of a child having cystic fibrosis from a woman with the disorder and a heterozygous asymptomatic man?

• A. 25%
• B. 50%
• C. 75%
• D. 100%

Answer: (B)

To determine the probability of a child having cystic fibrosis from a woman with the disorder and a heterozygous asymptomatic man, we have to consider how cystic fibrosis is inherited. Cystic fibrosis is an autosomal recessive disorder, which means that a person must inherit two copies of the faulty gene (one from each parent) to express the disease.

In this scenario, the woman has cystic fibrosis, meaning her genotype is homozygous recessive (ff). The heterozygous asymptomatic man has one normal allele and one cystic fibrosis allele (Ff). When we create a Punnett square for these two individuals, we will evaluate the possible genotypes of their offspring.

The possible combinations from the parent's genotypes are as follows:

• The woman can only contribute an f (cystic fibrosis allele).

• The man can contribute either F (normal allele) or f (cystic fibrosis allele).

This leads to the following genotype combinations for their children:

1. Ff (normal carrier)

2. ff (cystic fibrosis)

From this, we can see there are two possible genotypes for the children: 50% will be carriers of the cystic fibrosis allele (Ff) and