Human blood groups are governed by three alleles, ia, ib, and i. ia and ib are codominant and i is recessive to both. a man who has type b blood and a woman who has type a blood could have children of which of the following phenotypes?

They could have all four type phenotype that are A, B, AB, and O

Explanation:

If the man has A blood group and the woman has B blood group then the genotype of man can be IAIA or IAi and the genotype of woman can be IBIB or IBi.

               IA      i

       IB   IAIB   IBi

       i     IAi       ii

So if the genotype of the parents are IAi and IBi then out of four offspring one could have AB blood group, second could have B blood group, third could have A blood group and fourth could have O blood group as shown in the cross above.