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 IOIO.
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.
