Final answer:
The ABO blood group system is an example of multiple alleles, where IA, IB, and I alleles determine the blood type, and codominance, with both IA and IB alleles equally expressed in type AB individuals.
Step-by-step explanation:
The ABO blood group system is an example of multiple alleles and codominance in human genetics. Within this system, the three alleles are IA, IB, and i. The presence of IA or IB can code for A or B antigens on the surface of red blood cells, with IA and IB being codominant alleles, both expressed when present together in an AB individual. However, these alleles are both dominant over I, which codes for the absence of antigens and the O blood type. Therefore, an individual with IAi or IBi genotype will express phenotypes A or B, respectively, since A and B alleles mask the expression of the I allele, which depicts dominance.
The ABO blood groups are classified into A, B, AB, and O based on the genetics that determine the specific antigens present on the surface of red blood cells. When two parents with heterozygous A (IAi) and B (IBi) genotypes mate, their offspring can have any combination of ABO blood types, including the possibility of type AB, in which both A and B antigens are equally expressed on the red blood cells due to the codominant nature of the IA and IB alleles.