If a recessive disease appears only when both factors are recessive, why does risk increase when both parents are carriers?

Correct answer: Both parents can pass the recessive factor

The governing concept is recessive inheritance. A carrier usually has one normal dominant allele and one recessive disease allele, so the disease is not expressed. If both parents are carriers, each can pass the recessive allele to a child; the child may receive two recessive alleles and express the disease. In a simple autosomal case, the probability is 1 in 4 for each pregnancy, so option A is correct.