Solve the blood grouping question: A man having blood group A marries with a woman having blood group O. They have a child. What will be the blood group of the child?

The man having blood group A possess two possibilities of antigen present in the blood:      I^AI^A or I^AI^O

Similarly, the woman with blood group O has no antigen present in the blood: I^OI^O

The possible antigens present in the blood of their child is

                                                                                                 I^AI^A X I^OI^O                                   I^AI^O  X  I^OI^O

                                                                                                 I^AI^O and I^AI^O                                I^AI^O and I^OI^O

Thus, if man is homozygous, with both dominant gene A present in the blood (I^AI^A), there is a 100% possibility that child will be heterozygous, with blood group A (Possessing antigen I^AI^O).

But, if the man is heterozygous, with blood antigen (I^AI^O), then the calculated possibility of blood group of child will be:

  50% blood group A (with antigen I^AI^O) and 50% chance of blood group O (with no antigen I^OI^O)