The blood types A, B, AB, and O are the result of multiple allelic inheritance.

Here's why:

* Multiple Alleles: The ABO blood group system is controlled by a single gene, but this gene has *three* possible alleles: I^A, I^B, and i.

* Dominance: I^A and I^B are codominant, meaning they both express their traits when present together (resulting in AB blood type). The i allele is recessive, meaning it only expresses its trait (O blood type) when paired with another i allele.

Let me know if you'd like a more detailed explanation of how these alleles interact to produce the different blood types!