Blood groups are based on: A) the presence of inherited antigens on the surfaces of leukocytes and other nucleated cells. B) the presence of inherited antigens on the surfaces of erythrocytes. C) the presence of inherited circulating antibodies. D) the presence of induced circulating antibodies. E) All of these are correct.

Answer: B) the presence of inherited antigens on the surfaces of erythrocytes.

Explanation:

A blood group is a classification of the blood according to the characteristics present on the surface of the red blood cells called erythrocytes. The two most important classifications for describing blood groups in humans are antigens (the AB0 system) and the Rh factor.

The AB0 system was discovered in 1901, and was the first known blood grouping system; its name comes from the three types of groups that are identified: antigen A, antigen B, and 0 (zero) without antigens.

Each individual has a different set of erythrocyte antigens, and because of their number - there are currently 32 known antigenic systems, plus some differentiated antigens that have not yet been attributed to any specific system - it is difficult to find two individuals with the same antigenic composition. Different antigenic systems are characterized by inducing antibody formation at different intensities; therefore some are more common and others are more rare. So, the antigenic systems considered most important are the AB0 system and the RH system.

Characteristics of the AB0 system are:

People with type A blood: their red blood cells express type A antigens on their surface and develop antibodies to the B antigens in the plasma. People with type B blood: their red blood cells express type B antigens on their surface and develop antibodies to the B antigens in the plasma. Persons with type 0 blood: they have no such antigens (A or B) on the surface of their red blood cells, but develop antibodies to both types. Persons with type AB blood: having both antigens on the surface of their red blood cells, they do not make any antibodies to the A or B antigen.

The Rh system is the second blood group system in human blood transfusion with 50 antigens currently. In 1940, another group of antigens was discovered and they were called Rhesus factors (Rh factors). People with rhesus factors in their blood are classified as "Rh positive", while those without the factors are classified as "Rh negative". It is common for D-negative individuals to have no anti-D IgG (immunoglobulin-G) or IgM antibodies, since anti-D antibodies are not normally produced by sensitization to environmental substances. Rh-negative people form antibodies to the Rh factor, if they are exposed to Rh-positive blood.