In human blood grouping, the term ABO is used instead of ABC because O refers to:

Question

Accepted Answer

The correct option is 1:

In the ABO blood grouping system, the letters A and B refer to the specific antigens present on the surface of an individual's red blood cells (RBCs). Antigens are essentially markers that the immune system uses to recognize what belongs to the body and what doesn't. When we talk about blood type A, it means the individual has A antigens on their RBCs. Similarly, blood type B means they have B antigens. Blood type AB means both A and B antigens are present. Now, for blood type O, the 'O' actually signifies the *absence* of both A and B antigens on the red blood cell surface. This lack of A and B antigens is what makes type O blood unique and is why type O individuals are considered "universal donors" in transfusions, as their red blood cells won't trigger an immune response from anti-A or anti-B antibodies in the recipient.

The incorrect option is 2: Other antigen besides A and B.
The 'O' in ABO blood grouping specifically refers to the *lack* of A and B antigens. While other antigens exist on red blood cells (like Rh factor), the ABO system focuses solely on the presence or absence of A and B antigens. Therefore, 'O' does not refer to the presence of some other antigen within this specific classification.

The incorrect option is 3: Overdominance of its genes over A and B.
Blood type inheritance in the ABO system involves multiple alleles (IA, IB, and i) and exhibits codominance for A and B alleles, and complete dominance of both A and B over the O allele (i). The 'O' phenotype results from having two recessive 'i' alleles (ii), not from an overdominance of its genes.

The incorrect option is 4: One antibody, either anti-A or anti-B.
Individuals with type O blood produce *both* anti-A and anti-B antibodies in their blood plasma, not just one. These antibodies are crucial for identifying and reacting to foreign A or B antigens if they enter the bloodstream. The presence of both antibodies is a defining characteristic of type O blood in terms of its plasma components.