Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene. If both parents are asymptomatic carriers (heterozygotes), what is the probability that their first child will be an unaffected carrier?
Answer and explanation
Correct answer: A. 50%
For a cross between two carriers (Cc x Cc), the offspring probabilities are 25% homozygous dominant (CC, unaffected non-carrier), 50% heterozygous (Cc, unaffected carrier), and 25% homozygous recessive (cc, affected). Therefore, the probability of having an unaffected carrier child is 50%.
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