Final answer:
The AB blood type results from the codominant expression of the IA and IB alleles in the genotype IAIB. This allows for the presence of both A and B antigens on red blood cells, distinguishing it from incomplete dominance. Additionally, the ABO system is an example of multiple alleles.
Step-by-step explanation:
In blood, the genotype IAIB produces the phenotype AB blood. This is an example of codominance, because both the IA and IB alleles are expressed equally in AB blood types, leading to the production of both A and B antigens on the surface of red blood cells. This phenomenon of codominance differs from incomplete dominance, where an intermediate phenotype would be observed, rather than both phenotypes being expressed simultaneously and distinctly.Moreover, the ABO blood type system is also an example of multiple alleles, as there are three alleles (IA, IB, and i) that determine the blood type, though an individual inherits only two of these alleles. The AB blood type, specifically, demonstrates that neither IA nor IB is recessive when both are present, unlike the i allele, which is recessive to both.