Question

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits blood group A or O is dominant? Why or why not?

Answer 1

The information is insufficient to tell whether the trait - ‘A’ or ‘O’ is dominant. In case I let us assume that trait ‘A’ is dominant. Then father may have IAIA or IAIO and mother I^OI^O.

In this case, 50 per cent of the progeny will have blood group A and 50 percent of the progeny will have blood group O, when father’s blood group is A and mother’s is O.
In case II, let us assume that trait ‘O’ is dominant.
In this case also, we see that child may have blood group O
.Since, in both the assumptions the child can have blood group O, so we cannot establish which trait is dominant.