ABSTRACT
Prior to DNA analysis, biological material was characterized into a specic group to narrow the possible origin. ABO blood typing was used to classify blood based on the antigens present on the red blood cells. A person’s blood is classied as A, B, AB, or O corresponding to blood cells with antigen A, B, A and B, or none, respectively. Each blood type has an antibody that opposes the antigen not present in the red blood cells for the specic blood group. For example, type A blood possesses the A antigen and the anti-B antibody. The blood type of a specic blood sample can be determined by mixing a blood antibody and antigen and when the same type of antibody and antigen are combined, the blood will clump together. Therefore, when type A blood is exposed to anti-A antibody, the blood will clump. This explains why people with type A blood cannot receive transfusions of type B blood and vice versa. The table below summarizes the blood groups in the ABO system and their corresponding antigens and antibodies.
