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?
Are both Jane and Bill carriers?
I got 1/4 (25%) but I'm not sure if this is the answer.
3 answers
sS xsS>>ss sS Ss SS yes 1:4
thank you
Wait I think the answer may be 1/9
It is possible that both Jane and Bill could be homozygous for the dominant trait and not have cystic fibrosis. Jane and Bill may not be carriers.
However
There is a 2/3 chance Bill could be a carrier.
There is a 2/3 chance Jane could be a carrier.
If Jane and Bill (both as carriers) has a child there is a 1/4 chance from them having a child with cystic fibrosis
Multiplying all the probabilities, 2/3 X 2/3 X 1/4 = 1/9
It is possible that both Jane and Bill could be homozygous for the dominant trait and not have cystic fibrosis. Jane and Bill may not be carriers.
However
There is a 2/3 chance Bill could be a carrier.
There is a 2/3 chance Jane could be a carrier.
If Jane and Bill (both as carriers) has a child there is a 1/4 chance from them having a child with cystic fibrosis
Multiplying all the probabilities, 2/3 X 2/3 X 1/4 = 1/9