Awoman with type o blood is expecting a child. her husband is type a. both the woman's father and her husband's father had type b blood. what is the probability that the child will have type o blood?

Woman's genotype: ii
Husband's genotype: I^A i
-> possible husband's father genotypes are two I^B and I^B i
-> if husband's father has two I^B alleles, the husband will have one I^B allele present, which is not the case. So, there is i allele present. (can also infer that I^A comes from husband's mother)

Child's possible genotypes:
ii, ii, I^A i, I^A i
probability is 1/2