Explanation

In ABO blood group system, inheritance of grouping is controlled by a single autosomal gene on chromosomal-9 with three major alleles A, B, an O $\left( I^{A},I^{B}\ and\ I^{O} \right).$ The ABO blood group system has at least 6 alleles. On the basis of presence or absence of antigens and antibodies four blood groups (phenotypes) have been differentiated-A, B, AB and O blood groups. The phenotype, genotype, antigen and antibody of blood group ABO. [table] Phenotype | Genotype | Antigen | Antibody ; A | $I^{a}I^{o},I^{a}I^{a}$ | A | b ; B | $I^{b}I^{o},I^{b}I^{b}$ | B | a ; AB | $I^{a}I^{b}$ | A, B | None ; O | $I^{o}I^{o}$ | None | a, b [/table]