Final answer:
In the ABO blood system, multiple alleles refer to the three distinct alleles IA, IB, and i leading to six possible genotypes and four phenotypes (A, B, AB, and O). Alleles IA and IB are codominant, while both are dominant over i, which is significant in blood transfusions.
Step-by-step explanation:
Multiple alleles occurs in the ABO blood system, where there are three distinct alleles in human populations: IA, IB, and i. Each person inherits one allele from each parent, leading to six possible genotypes. Genotype IAIA or IAi produces type A blood, genotype IBIB or IBi produces type B blood, genotype ii results in type O blood, and genotype IAIB results in type AB blood, which demonstrates codominance, as both A and B antigens are equally expressed.
The ABO system has a critical role in blood transfusions, where type O individuals are universal donors, and type AB individuals are universal recipients. The IA and IB alleles are codominant with each other and dominant over the i allele, resulting in four blood types: A, B, AB, and O. This example of multiple allelism and dominance interactions is a fundamental concept in genetics and important in medical contexts like blood transfusion compatibility.