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MCAT Biology – Genetics
- by
- Feb 11, 2015
- MCAT Biology, MCAT Blog, MCAT Question of the Day
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%
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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