N. Saitou et F. Yamamoto, EVOLUTION OF PRIMATE ABO BLOOD-GROUP GENES AND THEIR HOMOLOGOUS GENES, Molecular biology and evolution, 14(4), 1997, pp. 399-411
There are three common alleles (A, B, and O) at the human ABO blood gr
oup locus. We compared nucleotide sequences of these alleles, and rela
tively large numbers of nucleotide differences were found among them.
These differences correspond to the divergence time of at least a few
million years, which is unusually large for a human allelic divergence
under neutral evolution. We constructed phylogenetic networks of huma
n and nonhuman primate ABO alleles, and at least three independent app
earances of B alleles from the ancestral A form were observed. These r
esults suggest that some kind of balancing selection may have been ope
rating at the ABO locus. We also constructed phylogenetic trees of ABO
and their evolutionarily related alpha-1,3-galactosyltransferase gene
s, and the divergence time between these two gene families was estimat
ed to be roughly 400 MYA.