Genetics Probability (Autosomal Recessive)

[protractor]

Homework Statement

Jane and Bill are married. Each of them has a brother with cystic fibrosis, which is autosomal recessive. Neither Jane, Bill or any of their parents have the disease. Based on this information, what is the probability that if this couple has a child, the child will have cystic fibrosis?

Relevant Equations

Cystic fibrosis is autosomal recessive.

I think both Jane and Bill are carriers. I'm unsure if the answer is 1/4 (25%).

 

[mjc123]

Why not show the working that leads to your answer of 1/4, and say why you are unsure about it?

 

[protractor]

Wait I think the answer could be 1/9.
It could be possible that Jane and Bill may not be carriers.
There is only 2/3 chance for each to be a carrier.

If both are carriers, then there is a 1/4 chance Jane and Bill's child could have cystic fibrosis.

Multiplying,
2/3 X 2/3 X 1/4 = 1/9

 

[epenguin]

I agree with your reasoning.

At first I didn't , it can be tricky.