ABO (ABO blood group )

The ABO blood groups were discovered by Karl Landsteiner in 1900, and its Mendelian hereditary system was established by Bernstein in 1924.  Yamamoto et al. (1990) eventually determined the cDNA sequences of three major human ABO blood group gene alleles.  Because the allelic distribution of non-human primate ABO blood group locus was already examined using immunological techniques, partial nucleotide sequences of chimpanzee, gorilla, and other non-human primate ABO blood group genes were soon determined by Yamamoto and other reserchers (e.g., Kominato et al., 1992).  While humans have A, B, and O alleles, chimpanzees have only A and O,  gorilla appear fixed with B alleles, then phylogenetically more remotely related orangutans have A, B, and O alleles like humans (Blancher et al., 1997).  Saitou and Yamamoto (1997), applied phylogenetic network techniques to ABO blood group nucleotide sequence data, and proposed that the common ancestor of both hominoids and Old World monkeys had A type allele, and that the B alleles then independently emerged in humans, gorillas, and in some Old World monkey lineages, by accumulating two nonsynonymous substitutions.  Because of large coalescence times among human A, B, and O alleles, as well as independent emergence of B alleles, this ABO blood group locus is probably under positive Darwinian balancing selection.  While some roles in modulating microbial infections are suggested, the real biological mechanisms for balancing selection are still not clear.