As described above, one remarkable result

of the analysis of the GM polymorphism is the observation of abrupt frequency changes between different continental areas worldwide. By subdividing the world into 10 continental or sub-continental regions (sub-Saharan Africa, North Africa, Europe, West Asia, Northeast Asia, Southeast Asia, Oceania, Circum-Arctic, North and Central America, and South America), we found a proportion of genetic diversity due to differences among regions of about 39%.12 This is much higher click here than generally found (albeit based on a different subdivision of the world and different numbers of groups) for allozymes and DNA markers, of the order of 10–15%,22–24 and 3–7% for most HLA loci.25 Extreme values (up to 88%) of human genetic diversity among the main geographic regions have only been found for strongly selected biological traits like skin pigmentation, whereas craniometric

traits also fall within the range of neutrally evolving genetic markers.26,27 We may ask ourselves whether, because of the immunological function of IgG molecules expressing GM allotypes, the GM polymorphism is subject to some kind of (directional) selection. Indeed, some studies have suggested that GM haplotypes were involved in susceptibilities to autoimmune diseases (see ref. 28,29 learn more for a review) and infectious diseases like malaria30–32 or filariasis.33 However, conclusive evidence

for disease associations has not been found. Moreover, we did not detect any departure from selective neutrality by using Ewens–Watterson’s tests (with Bonferroni’s correction) on 82 populations tested for GM worldwide.12 Therefore, our explanation of the unusual apportionment of genetic diversity observed for the GM polymorphism is, first, that this system has been tested by serological typing, thereby providing only a broad description of its molecular variation, and, second, as explained above, that the frequencies of the most frequent haplotypes PI-1840 in each geographic region are over-estimated because most GM frequencies were estimated by following a parsimonious approach considering a minimum number of haplotypes deduced ‘by hand’ from the phenotypic distributions. As a consequence, the proportion of genetic variation observed among regions has probably also been over-estimated. On the other hand, the most frequent GM haplotypes defined by serology may be seen as broad GM haplogroups including phylogenetically related haplotypes, an interpretation that is sustained by previous analyses performed at the DNA sequence level34 and that recalls the definition of Y-chromosome (non-recombining region, or NRY) haplogroups.35 The Y-chromosome markers deviate from other DNA markers in being, like GM, highly structured at the global scale: according to Hammer et al.