ABO blood groups in human population is controlled by three different alleles of the gene (I). How many genotypes and phenotypes respectively could exist in human population with respect to this?

Human blood group is controlled by 3 alleles i.e. I^A, I^B and i.

6 types of possible genotypes are I^AI^A, I^BI^B, I^AI^B, I^Ai, I^Bi and ii.

The genotypes I^AI^A  and I^Ai  reflect the  phenotype A blood group

The genotypes I^BI^B and I^Bi  reflect the phenotype B blood group

The genotype I^AI^B for the phenotype  AB blood group

The genotype ii for the phenotype O blood group.