The gene I that determines ABO blood groups has three alleles IA,IB and IO . The correct sequence of dominance of these alleles is
IA=IB>IO
ABO blood grouping in human beings is controlled by a gene I which has three alleles- IA,IB and IO. Among these, IA and IB are equally dominant indicating codominance, and they are dominant over IO or i, which is a recessive allele.