Question

In humans cystic fibrosis is a recessive genetic disorder that causes

mucous to build up in the lungs and digestive tract. A healthy couple has
their first child and later discover that the baby has cystic fibrosis. How is
it possible that two parents without the disorder can have a child with the disorder?

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Answer 1

If the parents were both carriers.

Step-by-step explanation:

Since cystic fibrosis is a recessive genetic disorder, two of the same alleles must be present in order to show, so.. for example, the genotype would be cc. The parents without the disorder must've been carriers, and their genotype would be Cc.

If you do a punnet square, Cc x Cc = 25% cc, 50% Cc, and 25% CC.