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A married couple is screened to assess the risk for
Tay-Sachs disease in their children. The activities of
hexosaminidase A in the sera of the mother and father
are 45% and 55%, respectively, of the reference value.
The couple has one child. What is the probability of the
child possessing one or more alleles of the Tay-Sachs
mutation?
(A) 0
(B) 0.25
© 0.5
(D) 0.75
(E) 1.0

D) 0.75 correct me if i'm wrong

ans is b

can some one explain the answer

I would think D. Each parent seems to be a carrier (partial enzyme activity), and Tay-Sachs is an autosomal recessive disease. So there's a 25% chance of the child having the disease, and a 50% chance of the child being a carrier = 75%