I got this question wrong I put 1/9 and 4/9 chance. Can someone tell me the answ
ID: 51415 • Letter: I
Question
I got this question wrong I put 1/9 and 4/9 chance. Can someone tell me the answer amd how they got the right answer. Thanks
Will and Deanna went to see a genetic counselor because each had a sibling affected with cystic fibrosis. (Cystic fibrosis is a recessive disease, and neither member of the couple nor any of their four parents is affected. CF+ = normal allele; CF = cystic fibrosis allele)
What are the chances that their child will be affected with cystic fibrosis and what is the probability that their child will be a carrier of the cystic fibrosis mutation?
Explanation / Answer
1) What are the chances that their child will be affected with cystic fibrosis ?
The condition for the child to be affected is that, both the parents should be carriers. The probability that each parent is a carrier is 2/3 and the chance of having an affected child by these parents is 2/3 x 2/3 x 1/4=1/9.
2. What is the probability that their child will be a carrier of the cystic fibrosis mutation?
The child will be a carrier, only if it had a heterozygous genotype of CFCF+
This could happen under two condition
a) Both parents are heterozygous, then the probability is 2/3 x 2/3 x 1/2=2/9
b) If one parent is heterozygous the probability is (Condition for both the male and female parent) 2/3 x 1/3 x 1/2 + 1/3 x 2/3 x1/2 = 2/9
Thus the probability is 2/9+2/9=4/9
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