What is the probability that a child will be affected by cystic fibrosis if both parents are carriers?

Cystic fibrosis is a genetic disorder caused by mutations in the CFTR gene, and it follows an autosomal recessive inheritance pattern. This means that for a child to be affected by cystic fibrosis, they must inherit two copies of the mutated gene—one from each parent.

When both parents are carriers of the cystic fibrosis gene, they each have one normal copy of the gene and one mutated copy. In this scenario, we can represent the normal gene as "N" and the mutated gene as "n". The possible combinations of alleles that the child can inherit can be visualized using a Punnett square:

1. NN - the child inherits both normal genes (normal, not a carrier).

2. Nn - the child inherits one normal gene and one mutated gene (carrier, not affected).

3. nN - the child inherits one normal gene and one mutated gene (carrier, not affected).

4. nn - the child inherits both mutated genes (affected by cystic fibrosis).

From this, we can see that out of the four possible combinations, only one combination (nn) results in the child being affected by cystic fibrosis. Therefore, the probability that a child will