Human blood is grouped into four main types (or groups): A, B, AB and O.

Little less than half the population of the planet (about 48%) have type O blood, which makes it the most common group. The blood group of a child is determined by the parents' genes he or she inherits. Antigens are proteins which are found on the surface of red blood cells. In the process of blood type determination, these biomolecules represent the main characteristic criterion. If one has the antigen B on the red blood cells, then he or she has got type B blood.

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