The gene controlling the ABO blood groups in humans is:

I

The correct answer is Option (3) → I

ABO blood groups are controlled by the gene I. The gene (I) has three alleles I ^A , I ^B and I. In this system, individuals can possess red blood cells categorized as type A (I^A), type B (I^B), 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 (I^AI^A) or a combination of one A allele and one O allele (I^Ai). Similarly, type B blood is determined by either two B alleles (I^BI^B) or one B allele and one O allele (I^Bi). 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.