Asked Mar 9, 2020

A young couple went to see a genetic counselor because each had a sibling with cystic fibrosis. (Cystic
fibrosis is a recessive disease, and neither member of
the couple nor any of their four parents is affected.)
a. What is the probability that the female of this
couple is a carrier?
b. What are the chances that their child will have
cystic fibrosis?
c. What is the probability that their child will be a
carrier of the cystic fibrosis disease allele?


Expert Answer

Step 1

(a) The probability of the female of this couple is a carrier:

If the female of this couple has a sibling with Cystic fibrosis, then her parents must be heterozygous for this disease,

Biology homework question answer, step 1, image 1

Progeny with genotype (cfcf) is the affected sibling of the female. So, the probability of the female partner having heterozygous (carrier) for Cystic fibrosis is 2 out of 3. That means the probability is 2/3.

Step 2

(b) Chances that their child will have Cystic fibrosis:

      The child will be affected with Cystic fibrosis, if its genotype will be cfcf.

The chance of either parent is a ...

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