There is a high likelihood that you know of which ABO blood group you belong to. I am A. My daughter is A. My father is B. My mother is A. I have siblings who are A, O, B, and AB. The inheritance is roughly Mendelian, with O being “recessive” to A and B (which are co-dominant with each other, ergo, AB). It is also generally common knowledge that O is a “universal donor,” while A and B can only give to individuals within their respective blood group and AB.
Because ABO was easy to assay it was one of the earliest Mendelian markers utilized in human genetics. In the first half of the 20th century while some anthropologists were measuring skulls, others were mapping out the frequency of A, B, and O. Today with much more robust genetic methods ABO has lost its old luster as a genetic marker, especially since there is a strong suspicion that the variants are strongly shaped by natural selection. This makes them only marginally useful for systematics, which rely upon loci which are honest mirrors of demographic history.