If both parents are carriers of the cystic fibrosis gene, what is the probability that their child will have cystic fibrosis?

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Multiple Choice

If both parents are carriers of the cystic fibrosis gene, what is the probability that their child will have cystic fibrosis?

Explanation:
This question hinges on autosomal recessive inheritance. If both parents are carriers, each parent has one normal allele and one cystic fibrosis allele (A, a). The child’s possible genotypes are AA, Aa, Aa, and aa. Only the aa combination causes cystic fibrosis, so there is a 1 in 4 chance, i.e., 25%, that the child will have the disease. The other outcomes are AA (unaffected non-carrier) or Aa (carrier) with 25% and 50% frequencies, respectively.

This question hinges on autosomal recessive inheritance. If both parents are carriers, each parent has one normal allele and one cystic fibrosis allele (A, a). The child’s possible genotypes are AA, Aa, Aa, and aa. Only the aa combination causes cystic fibrosis, so there is a 1 in 4 chance, i.e., 25%, that the child will have the disease. The other outcomes are AA (unaffected non-carrier) or Aa (carrier) with 25% and 50% frequencies, respectively.

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