Question

One parent is a cystic fibrosis carrier, and the other has

nocystic fibrosis gene. Find the probability of each of
thefollowing.
a.) The child would have cystic fibrosis.
b.) The child would be a carrier.
c.) The child would not have cystic fibrosis and not bea
carrier.
d.) The child would be healthy (i.e., free ofsymptoms).

Answer 1

A - 0%

B- 50%

C- 50%

D- 100%

Explanation:

Cystic fibrosis is inherited in an autosomal recessive form, meaning that a person has to inherit two abnormal genes for the disease to manifest. In the case of this question, one parent is a gene carrier, so his genotype is Aa, while the other does not have the cystic fibrosis gene, so AA.

Performing the cross of Aa x AA, we can see that:

a.) The probability of a child would have cystic fibrosis is 0%, since the disease is recessive and to be affected it should receive a recessive gene from each parent.

b.) The probability of a child would be a carrier is 50%, as 50% of the crossing phenotypes are Aa.

c.) The probability of a child would not have cystic fibrosis and is not a carrier is 50%, as 50% of the child's genotype is AA.

d.) The probability of a child would be healthy is 100%, as of all possible phenotypes none is affected.