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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?

A

$\left(\cfrac{1}{2}\times\cfrac{1}{2}\times\cfrac{1}{4}\right)^2=0.003906=3.906\times10^{-3}$

B

$\left(\cfrac{2}{3}\times\cfrac{2}{3}\right)^2=0.1975=1.975\times10^{-1}$

C

$\left(\cfrac{2}{3}\times\cfrac{1}{3}\times\cfrac{1}{4}\right)^2=0.00308=3.08\times10^{-3}$

D

$\left(\cfrac{2}{3}\times\cfrac{1}{2}\right)^2=0.333303.333\times10^{-1}$

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