If someone who is heterozygous for (or a carrier of) a recessive genetic disease has a child with a homozygous NON-carrier, what are the chances that the child will have (come down with) the disease? (Feel free to make an inheritance diagram on scratch paper if it will help you to think this through.)

Question

Quizplus · Accepted Answer

Since the disease is recessive, a child can only have the disease if they inherit two copies of the recessive allele, one from each parent. A heterozygous carrier has one normal allele and one disease allele, while a homozygous non-carrier has two normal alleles. Therefore, any child from this pairing will have a 0% chance of having two recessive alleles necessary for the disease to manifest, as they will always inherit at least one normal allele from the homozygous non-carrier parent.

If Someone Who Is Heterozygous for (Or a Carrier Of)