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On the surface of red blood cells are proteins known as antigens, which interact closely with white blood cells, the body’s defense against infection. Antigens function as identifying markers, enabling the immune system to recognize which cells belong in the body versus those that are foreign invaders. The two primary types of antigens that determine blood type are A and B.
The Genetics of Blood Types
The existence of four distinct blood types—A, B, AB, and O—can be traced back to the influence of three different alleles of a specific gene. The alleles determine whether the A or B antigens are present on the red blood cells. The A and B alleles code for their respective antigens, while the O allele does not code for either.