What are the four major blood groups?
A, B, AB, and O are the four major blood groups.
The four major blood groups in human beings are based on the presence of specific surface antigens known as A and B. These antigens have strong antigenicity - that is, they evoke a strong antibody reaction.
The presence of the A surface antigen renders that blood group A.
The presence of the B surface antigen renders that blood group B.
The presence of both surface antigens renders that blood group AB.
The presence of neither surface antigen renders that blood group O.
The presence or absence of the Rh (or D) antigen makes the group Rh positive or Rh negative, thus subdividing the four blood groups into eight sub-types.