A girl with diabetes mellitus (a recessive trait) and a short-sighted (dominant trait) boy get married.

A girl with diabetes mellitus (a recessive trait) and a short-sighted (dominant trait) boy get married. Which children can they have if the boy is homozygous? Will they have perfectly healthy grandchildren if their children are married to persons with diabetes and normal vision?

Let the gene for normal vision be A, and the gene for myopia a. The diabetes gene will be b, the normal gene will be B. Genotype of women: AAbb, boys: aaBB.

Genotype of children: AaBb. The genotype of their mating partners with normal vision, AAbb diabetic patients. Genotypes of grandchildren: AABb, Aabb.

The children will be nearsighted but will not suffer from diabetes. 50% of grandchildren will have normal vision if the children are married to persons with normal vision (since all children have a normal vision gene from a woman, which will be passed on to half of her grandchildren). Since diabetes is a recessive trait, the woman is homozygous for it, since diabetes is manifested. All her children will have a diabetes gene, but they will not get sick, so they will get the allele of the normal gene from their father. As for the grandchildren from the marriage of the children of this woman and diabetics, half of them will have diabetes.