Chapter 3, Problem 25ESP

Tay–Sachs disease (TSD) is an inborn error of metabolism that results in death, often by the age of 2. You are a genetic counselor interviewing a phenotypically normal couple who tell you the male had a female first cousin (on his father’s side) who died from TSD and the female had a maternal uncle with TSD. There are no other known cases in either of the families, and none of the matings have been between related individuals. Assume that this trait is very rare.

1. (a) Draw a pedigree of the families of this couple, showing the relevant individuals.
2. (b) Calculate the probability that both the male and female are carriers for TSD.
3. (c) What is the probability that neither of them is a carrier?
4. (d) What is the probability that one of them is a carrier and the other is not? [Hint: The p values in (b), (c), and (d) should equal 1.]