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PCAT Biological Processes – Genetics

Cystic fibrosis is an autosomal recessive disease that causes severe breathing difficulties and a number of other symptoms. If a male and female, both of whom are carriers for the disease, have one child, what is the probability that the child will also be a carrier?

A) 0%

B) 25%

C) 50%

D) 100%

Explanation
Cystic fibrosis is an autosomal recessive disease that causes severe breathing difficulties and a number of other symptoms. If a male and female, both of whom are carriers for the disease, have one child, what is the probability that the child will also be a carrier?

A) 0%

B) 25%

C) 50%

D) 100%

punnet square

The Punnett square for the cross in the question is shown above. Carriers are those with the genotype Aa, which are the two shaded squares. Thus the child has a 50% chance of being a carrier, a 25% chance of having the disease and a 25% chance of the wild-type AA.

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