Question

A person having $I^A{I}^B$ alleles would show ________ blood type and that is because of ____________ of alleles.

• A. AB, polygenic inheritance
• B. AB, incomplete dominance
• C. A, complete dominance
• D. AB, codominance

Answer 1

The correct option is D AB, codominance

Codominance is a phenomenon where neither of the alleles suppresses the phenotype of its heterozygous counterpart. Both alleles get expressed in the trait. This contradicts Mendel's genetic laws of inheritance. Not all genes have only two alternative alleles or versions to express their characters, there are many characters in a population that are governed by more than two alleles present in a population, and the phenomenon is called multiple allelism.

One of the important examples of multiple allelism is ABO blood typing is observed in human beings. ABO blood typing in humans is governed by the gene I, which has three variants- $I^A,I^B$ and i. When allele $I^A$ and i are there type A gets expressed and when $I^B$ and i are clubbed then B gets expressed but when both alleles are $I^A$ and $I^B$ are together in the same locus of the homologous chromosomes then both the alleles express themselves without suppressing the effects of any of either allele. This phenomenon is called codominance.