Final answer:
John's mom, with type B blood, can have two possible genotypes: homozygous (IBIB) or heterozygous (IBi). These determine the potential blood types of their offspring when coupled with John's dad's type O blood (genotype ii).
Step-by-step explanation:
The student has a question about the possible genotypes of John's mom who has type B blood. Since the ABO blood group system has three alleles, IA, IB, and i, and John's dad has type O blood (genotype ii), John's mom can have one of two different genotypes for type B blood. These genotypes are either homozygous (IBIB) or heterozygous (IBi). If John's mom has type B blood and John's dad has type O blood, their children could have blood types B or O depending on the genotype of the mom.