The grouping of blood is based on substances called

The red blood corpuscles or Erythrocytes usually carry antigens and there are two types of antigens. The A group persons have antigen A in their red corpuscles and the B group have antigen A in their red corpuscles.The AB group persons have both antigen A and antigen B in their erythrocytes.The 'O'group persons have no antigens in their red corpuscles.