The husband has blood type 0, his wife has blood type A, and the wife’s father has blood type 0.

The husband has blood type 0, his wife has blood type A, and the wife’s father has blood type 0. What is the probability that they will have children with blood type 0 and blood type A?

If the husband has the first blood group with the OO genotype, then any of his children will have the O gene. The wife has the second blood group, and her father has the first, which means she will have the AO genotype. Children from a given marriage will have the OO genotype, which corresponds to the first blood group, or the AO genotype, which corresponds to the second blood group. Therefore, from this marriage, children with the first and second blood groups can appear in an equal probability of 50%.