Question

Robert and his wife are ready to start a family, but they are concerned about having a child an inherited disease. This disease is a recessive disorder which requires both parents to contribute a recessive allele in order for the child to express the disorder. If both Robert and his wife are heterozygous for this trait, what is the probability that one of their children will have the disease?

Answer 1

The probability is 1/4

Both parents are heterozygous.

Aa + Aa

This will give the following possibilities for offspring genotype:

AA, Aa, Aa, aa

As you can see the chance of a offspring having 2 copies of the recessive allele (which is required for the offspring to have the inherited disease is only a 1 in 4 chance.