Question

Cystic fibrosis is one of the most common autosomal recessive disorders. The carrier frequency in a general population is 1/25. A woman who knows she is heterozygous for the mutation that causes cystic fibrosis (CF) marries a man with no family history of CF at all. What is the probability that they will produce a child that has cystic fibrosis? Suppose the couple above has a child with cystic fibrosis. What is the chance that their second child will have it? Remember to explain why.

im looking for the probabilities of each

Answer 1

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

carrier frequency = 1/25

so chance of father being carrier is =1/25

When mother and father are carriers for cystic fibrosis, the chances of child being affected is 1/4

probability that they will produce a child that has cystic fibrosis = 1/4 x 1/25 = 1/100

the chance that their second child will have it is same as the first child. Nothing has changed in terms of probability.