Tay-Sachs is a recessive autosomal disease that primarily affects Ashkenazi Jews and a few other populations. This disorder causes neurological deterioration during childhood due to a genetic mutation in the HEXA gene on chromosome 15 and an insufficient activity of the enzyme hexosaminidase A. Hexosaminidase A is a very crucial hydrolytic enzyme, located in the lysosomes, that catalyzes glycolipids.
A man with no symptoms of the disease whose maternal uncle had Tay-Sachs is trying to determine the probability that he and his wife could have an affected child. His father does not come from a high-risk population. His wife’s brother died of the disease at an early age.
What is the probability that the couple’s first two children will be affected with Tay-Sachs?