Blood groups, compatibilities and incompatibilities
The blood group describes the individual composition of proteins on the surface of the red blood cells of higher animals, especially humans. The surfaces differ in different proteins that function as antigenes. If the blood of different blood groups is mixed, the cells clump together because of the tie to antibodies. Therefore, before the discovery of blood groups, blood transfusions were only randomly successful and often deadly. Blood groups are inherited and thus can be used to prove family relationships, e.g. with the paternity exclusion test. For humans, there are about 20 different systems of blood group classification. The most important ones are the AB0 system and the Rhesus system.