Final answer:
A woman with type A blood (possibly IAi) and a man with type B blood (possibly IBi) can have a child with type O blood (ii) if both parents carry the recessive i allele and pass it on to their child.
Step-by-step explanation:
To understand how a woman with type A blood and a man with type B blood can have a child with type O blood, we need to look at the genetics of the ABO blood group system. The ABO blood types are determined by a single gene with three alleles: IA (A), IB (B), and i (O). The alleles IA and IB are codominant, meaning that if an individual inherits both, they will express both A and B antigens and have type AB blood. The allele i is recessive and does not produce any antigen. Therefore, for an individual to have type O blood, they must inherit two recessive alleles (ii).
A person with type A blood can be either homozygous (IAIA) or heterozygous (IAi), and similarly, a person with type B blood can have genotypes IBIB or IBi. If both the woman and man in question have heterozygous types, meaning their genotypes are IAi and IBi respectively, each parent carries the recessive allele i. In this case, there is a possibility that their child could inherit the i allele from each parent, resulting in the genotype ii, which manifests as type O blood. The potential blood types of the child from such a cross would be A, B, AB, or O, with each type having an equal chance of 25% if both parents are heterozygous.