Multiple alleles can be defined as a series of forms of a gene situated at the same locus of homologous chromosomes. According to Mendel, each gene had two alternate forms or allele morphs are being dominant and the other being recessive.
Multiple alleles are the alternative forms of the same gene so they influence the same trait. The wild-type allele is mostly dominant over the mutant alleles. The wild type is considered the standard and all other alleles are considered variants.
The ABO blood group antigens are attached to oligosaccharide chains that project above the RBC surface. These chains are attached to proteins and lipids that lie in the RBC membrane. The ABO gene indirectly encodes the ABO blood group antigens. The ABO locus has three main allelic forms: A, B, and O.
ABO blood group system, the classification of human blood based on the inherited properties of red blood cells (erythrocytes) as determined by the presence or absence of the antigens A and B, which are carried on the surface of the red cells. Persons may thus have type A, type B, type O, or type AB blood