There are four main blood types in the ABO blood group system defined by the presence or absence of antigens A and B. A person's blood type is determined by combinations of three alleles - IA produces the A antigen, IB produces the B antigen, and i produces no antigen. Both IA and IB are codominant, so someone with the genotype IAIB will have both the A and B antigens and have blood type AB.

1. Human Blood Groups

2. ABO Blood Group There are 4 blood types in ABO blood group system. Blood Group Antigen A A B B AB A and B O Nil

3. Inheritance of Blood types Human blood type is determined by co-dominant alleles. There are three different alleles. I A , I B and i I A and I B are the dominant alleles and ‘ i ’ is the recessive allele. Allele is one of the variant forms of a gene at a particular location, on a chromosome. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one).

4. Role of alleles I A produces A antigen I B produces B antigen i produces no antigen (recessive allele) I A and I B are co-dominant. That is, an individual with the genotype I A I B will produce both A and B antigens

5. Each of us has two blood type alleles. We inherit one blood type allele from our biological mother and one from our biological father. Genotype Blood Group A A B B AB O I A I A I A i I B I B I B i I A I B i i