ABO blood groupings are controlled by the gene I. This "ABO blood grouping in human beings is an example of -

Co-dominance

The correct answer is Option (3) → Co-dominance    

Co-dominance occurs when both alleles in a heterozygous individual contribute to the phenotype. In the case of the ABO blood group system, the IA and IB alleles are co-dominant. This means that if an individual has both IA and IB alleles (genotype IAIB), both alleles are expressed, and the individual has blood type AB, which has both A and B antigens on the surface of the red blood cells. A good example of co-dominance is different types of red blood cells that determine ABO blood grouping in human beings.