ABO blood group system each parent; each has a 25% chance, but some occur more than once. Historically, ABO blood tests were used in paternity testing, but in 1957 only 50% of American men falsely accused were able to use them as evidence against paternity. Occasionally, the blood types of children are not consistent with expectations—for example, a type O child can be born to an AB parent—due to rare situations, such as Bombay phenotype and cis AB. The A blood type contains about 20 subgroups, of which A1 and A2 are the most common (over 99%). A1 makes up about 80% of all
ABO blood group system life by sensitization to environmental substances, such as food, bacteria, and viruses. The ABO blood types were discovered by Karl Landsteiner in 1901, for which he received the Nobel Prize in Physiology or Medicine in 1930. ABO blood types are also present in some other animals such as rodents and apes, including chimpanzees, bonobos, and gorillas. The ABO blood types were first discovered by an Austrian Physician Karl Landsteiner working at the Pathological-Anatomical Institute of the University of Vienna (now Medical University of Vienna). In 1900, he found that blood sera from different persons would clump together (agglutinate) when mixed