ABO blood group system
Prior to the 1952 confirmation of DNA as the hereditary material by Alfred Hershey and Martha Chase, scientists used blood proteins to study human genetic variation. The ABO blood group system is widely credited to have been discovered by the Austrian Karl Landsteiner, who found three different blood types in 1900. Blood groups are inherited from both parents. The ABO blood type is controlled by a single gene (the ABO gene) with three alleles: "i", "IA", and "IB".