Alkaptonuria is a genetic disorder caused by a mutated gene that affects the homogentisic acid oxidase enzyme. The mutant gene has a different BamHI restriction site than the normal gene, resulting in a Ser-to-Thr missense mutation. If a heterozygous mother (Aa) for the mutant gene and a homozygous father (aa) for the mutant gene have children, what is the expected genotypic ratio of the offspring?