S
Sarah
Guest
A young couple went to see a genetic counselor because each had a sibling affected with cystic fibrosis. (Cystic fibrosis is a recessive disorder and neither member of the couple nor their parents is affected). What is the probability that their child will be a carrier of cystic fibrosis?
So, I know that both sets of parents are heterozygous for cystic fibrosis. This means that the man and women each have a 2/3 chance of being a carrier. If they are both carriers, there is a 2/3 chance that their child will be a carrier. So, I thought you would multiple the probabilities 2/3 x 2/3 x 2/3, to get 8/27, which would be the probability of their child being a carrier. However, the back of my book says the probability is 4/9 and I don't understand how they got that.
So, I know that both sets of parents are heterozygous for cystic fibrosis. This means that the man and women each have a 2/3 chance of being a carrier. If they are both carriers, there is a 2/3 chance that their child will be a carrier. So, I thought you would multiple the probabilities 2/3 x 2/3 x 2/3, to get 8/27, which would be the probability of their child being a carrier. However, the back of my book says the probability is 4/9 and I don't understand how they got that.