Question

A normal man marries either a colour blind or a carrier woman. Predict the kind of children which may be expected in both the conditions.

Answer 1

A normal man marrying a colour blind or carrier woman will have differing children:

1. If the woman is colour blind (XᴄXᴄ), all sons inherit the defective X from mother and normal Y from father, so all sons will be colour blind. All daughters inherit one defective X from mother and one normal X from father, so they will be carriers.
2. If the woman is a carrier (XᴄX), sons have a 50% chance of being colour blind or normal, daughters have a 50% chance of being carriers or normal.

Hence, colour blindness appears mainly in sons, while daughters are mostly carriers, except if the mother is homozygous colour blind. Fathers cannot pass the defective X to sons as sons inherit Y from their father.