[khanar]

A couple of Jews are about to marry. Both of them have siblings who died from a Tay Sach's disease. The frequency of heterozygotes in the Ashkenazi Jews is 0.1. The couple are asking what is the probability that they have a child affected by the disease?

a- 0.11
b- 0.25
c- 0.0025
d- 0.0625
e- 0.33

 

[khanar]

0.1 X 0.1 X 0.25 = 0.0025 answer D

 

[khanar]

0.1 X 0.1 X 0.25 = 0.0025 answer D

Your answer is not correct

 

[khanar]

Your answer is not correct

What is the correct answer then?

 

[khanar]

I think that each parent has 2/3 chance of being a carrier (since they have an affected sibling) so
2/3 X 2/3 X 1/4 = 4/36 = 0.11 (answer A)

You got the correct answer