The O2 allele : Questioning the phenotypic definition of an ABO allele
There are three main alleles in the ABO blood group system, A, B, and O. The former two alleles encode glycosyltransferases resulting in the wild-type A and B phenotypes, whereas the latter allele does not encode a functional enzyme owing to a frameshift polymorphism in the majority of cases. Thus the group O phenotype is the absence of A or B sugars. More than 15 years ago the O 2 allele was desc