Final answer:
The 'positive' or 'negative' in blood type refers to the presence or absence of the Rh antigen on the surface of red blood cells, with the Rh D antigen being the most clinically significant. This is separate from the ABO blood group system, which includes antigen A and antigen B.
Step-by-step explanation:
When an individual's blood type is described as "positive" or "negative," this refers to the presence or absence of the Rh antigen. For example, 'A positive' indicates that the Rh antigen is present on the red blood cells, while 'A negative' indicates its absence. People with the Rh D antigen are described as Rh positive, and those without it are Rh negative. This Rh factor is different from the ABO blood group system, but both play a critical role in blood transfusions and compatibility.
Blood type is determined by antigens on the surface of red blood cells, including the well-known ABO system and the Rh system. In the ABO system, the glycolipids known as antigen A and antigen B determine if someone is type A, B, AB, or O. The Rh antigen, specifically the Rh D antigen, is a separate system, and its presence or absence denotes the positive or negative sign in blood typing. This antigen was initially discovered in rhesus macaques, hence the name.