Question

what can be predicted about an individual if none of their children have a recessive genetic disorder?
they are homozygous dominant
they are carriers of the disorder
they are homozygous recessive

Explanation:

• If an individual is homozygous recessive (\(aa\)), they would express the recessive genetic disorder. Since none of their children have the disorder, this option is incorrect.
• If an individual is a carrier (\(Aa\)), and their partner is also a carrier (\(Aa\)), there is a \(25\%\) chance (\(\frac{1}{4}\)) of having a child with the recessive disorder (\(aa\)) according to Mendelian genetics (\(Aa\times Aa: AA:Aa:Aa:aa = 1:2:2:1\)). But the fact that none of the children have the disorder doesn't rule out the possibility of the individual being a carrier (it could be due to chance in a small sample of children).
• If an individual is homozygous dominant (\(AA\)), when they have children (assuming their partner has at least one dominant allele, which is reasonable as the child doesn't have the recessive disorder), all their children will have at least one dominant allele (\(A\)) from this parent. Since the recessive disorder is only expressed when an individual has two recessive alleles (\(aa\)), a homozygous - dominant individual (\(AA\)) can ensure that their children do not have the recessive disorder (assuming normal Mendelian inheritance and no new mutations).

Answer:

they are homozygous dominant