Answer:
The ABO blood group is the case of co-dominance or multiple allelism. Co-dominance may be defined as a non Mendelian inheritance in which both the alleles can express themselves in the heterozygous condition.
The person with blood type A has two possible genotypes with IA IA or IA i.
The person with blood type B has two possible genotype with IB IB or IBi.
The person with blood type has genotype of IAIB.
The person with blood type O has possible genotype is ii.
Thus, there are total six possible genotype of blood group exist in human population.