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.

Answer 1

The autosomal recessive disorder makes it 25% probability for the child to get the disease or carry the genes for CF. With each pregnancy, the child may or may not be affected by the disease as only the mother is heterozygote for it. The chances that the child will be produced with CF or cystic Fibrosis is around 25%. It is the carrier frequency.

Now lets us say the couple already have a child with cystic Fibrosis. The chances of the second child to have the disease also remain same because it depends on what genes are being inherited to the child. The child might get the gene for CF and it might be recessive or dominant. If it is recessive, the child do not suffer from the disease but carry the gene for it. If the child is dominant, the child carry the gene and also suffers from the disease.