Cystic fibrosis is caused by mutations in the CF gene, and there are several different mutations that are known to result in CF disease. The CF mutations behave as recessive alleles to the WT CF allele. If two carriers that have different mutations in their CF genes have children what is the probability that one of their children will have CF disease?
A) 100%
B) 25%
C) 50%
D) 75%

Question

Quizplus · Accepted Answer

Cystic fibrosis is an autosomal recessive disorder, meaning that an individual must inherit two copies of the defective gene (one from each parent) to manifest the disease. When both parents are carriers (each having one mutant allele and one normal allele), the probability of their child inheriting two mutant alleles (and thus having CF) is 25%. This is calculated using a Punnett square, where the possible genetic combinations for the offspring include one normal allele from each parent (25% chance), one mutant allele from one parent and one normal allele from the other parent (two possibilities, each with a 25% chance, totaling 50%), and one mutant allele from each parent (25% chance, resulting in CF).

Cystic Fibrosis Is Caused by Mutations in the CF Gene