ABO blood group is an example of :

Multiple alleles

The correct answer is Option (2) -Multiple alleles

Multiple allelism refers to a genetic condition where more than two contrasting characters are controlled by multiple alleles at a single genetic locus. With multiple alleles, there are more than two potential phenotypes based on the various dominant or recessive alleles present in the trait, as well as the inheritance patterns these alleles follow when combined.

An excellent illustration of multiple allelism in humans is the ABO blood type system. In this system, individuals can possess red blood cells categorized as type A (IA), type B (IB), or type O (i), representing three different alleles. These alleles can combine in various ways according to Mendel's Laws of Inheritance, resulting in genotypes that give rise to type A, type B, type AB, or type O blood. Type A blood arises from either two A alleles (IA IA) or a combination of one A allele and one O allele (IAi). Similarly, type B blood is determined by either two B alleles (IB IB) or one B allele and one O allele (IBi). Type O blood, on the other hand, is exclusively associated with two recessive O alleles (ii). These examples demonstrate instances of simple or complete dominance in the context of multiple allelism.