A man has Type A blood and his wife has type B blood. A physician types the blood of their four children and finds one of each of the four blood types among them. How is this possible?
The blood types A and B have two genotypes. For Blood type A, the genotypes are AA or AO. For blood type B, the genotypes are BB or BO. By doing punnett square of the possible combinations of the blood type of the parents, we can see that the genotypes of both parents are AO and BO.
B AB BO
O AO OO
25% AO or blood type A
25% BO or blood type B
25% AB or blood type AB
25% OO or blood type O
This confirms the results of the test done by the physician. It is possible if the father has a genotype of AO and the mother has a genotype of BO.