What percentage risk does a mother's son have of developing Huntington's disease if the mother is a carrier?

For a mother who is a carrier of Huntington's disease, there is a specific inheritance pattern to consider, as Huntington's disease is an autosomal dominant condition. This means that only one copy of the mutated gene is necessary for an individual to express the disease.

Since the mother is a carrier, she has one normal allele (the non-mutated form of the gene) and one mutated allele (the one that causes Huntington's disease). When she has children, there are two possible alleles that each child can inherit from her: the normal allele or the mutated allele.

For each child, there are thus two possible outcomes:

1. They inherit the normal allele, resulting in a child who does not have the disease and is not a carrier.

2. They inherit the mutated allele, resulting in a child who will develop Huntington's disease.

This means that for each son (or daughter), there is a 50% chance of inheriting the mutated gene and thereby developing the disease. Therefore, if the mother is a carrier of the Huntington's disease gene, her son has a 50% risk of developing the condition.