Read the given passage and answer the question.

ABO blood groups in human beings are controlled by the gene $I$. The plasma membrane of the red blood cells has sugar polymers that protrude from its surface and the kind of sugar is controlled by the gene. The gene ($I$) has three alleles $I^A, I^B$ and $i$. The alleles $I^A$ and $I^B$ produce a slightly different form of the sugar while allele $i$ does not produce any sugar. Because humans are diploid organisms, each person possesses any two of the three $I$ gene alleles. $I^A$ and $I^B$ are completely dominant over $i$.

Blood group 'AB' is an example of:

Co-dominance

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

Blood group AB is an example of co-dominance because both alleles I^A and I^B are expressed equally in the phenotype. In individuals with the I^AI^B genotype, both A and B antigens are present on the surface of red blood cells, rather than one being dominant over the other. This simultaneous expression of both alleles is characteristic of co-dominance.