Question

Explain the genetic basis of blood grouping in the human population?

Answer 1

Human blood inheritance is the best-known example of codominance and multiple alleles. It is governed by $3$ alleles namely ${I_A}$, ${I_B}$, and $I$. The ${I_A}$ and ${I_B}$ alleles are responsible for the production of A and B antigens, respectively. The allele ${I_A}$ for the A antigen is co-dominant with the allele${I_B}$for the B antigen. Both${I_A}$and ${I_B}$ are completely dominant to the allele$I$, which fails to specify A or B antigens.

Complete answer:
The plasma membrane of RBC contains many antigens. Based on the presence or absence of various antigens, blood groups are determined. There are at least $24$ blood groups. The most common ABO blood group (A, B, AB, and O) is based on the presence of ABO antigens.
The ABO antigens are complex oligosaccharides present in the form of glycoproteins and glycolipids. In the formation of A and B antigens, the H molecule (coded by H gene) acts as a precursor. In the case of A antigen, H contains an additional N-acetylgalactosamine, whereas in B antigen an additional galactose is linked to the H molecule. Individuals of type AB possess both A and B antigens and individuals of type O contain only H molecules.
Thus, the RBC of people with type A blood group contains A and H antigens, those with type B blood groups contain B & H antigens where those with type AB blood group have both A, B, and H antigens and those with type O blood group have only H antigen.

Note: Blood groups in humans depend upon the genes inherited by the offspring from the parents. In humans, $3$ different genes control the blood group. An individual can inherit only $2$ of these $3$ genes which determine his blood group.