Recently, Mirabal et al1 have noted that their results of Y-chromosome haplogroup (hg) N1b analysis challenge earlier findings2, 3 and suggest that N1b-P43 mutation may have occurred in the Uralic range rather than in Siberia and much earlier than has been proposed (12.9±4.1 instead of 5.2±2.7 kya). Mirabal et al performed high-resolution haplotyping of Y chromosomes from populations in the East European region of Russia and the Uralic mountains and compared them with relevant previously published data. Meanwhile, they did not find it possible to compare the data obtained with South Siberian data set, so we are intending here to make up this deficiency. In addition to the data obtained by Mirabal et al, we have used the data on hg N1b diversity of Northwest Siberian Khants and Mansi4 and Russian Pomors5 as well as our published data on N1b diversity in South Siberians (Altaians, Shors, Tuvinians, Tofalars, Sojots, Khakassians, Buryats, Mongolians and Kalmyks) and Central and Northeast Siberians (Yakuts, Evenks, Evens and Koryaks).3 In the latter study, 83 individuals were found as belonging to hg N1b. Median-joining analysis of 53 N1b haplotypes revealed in 168 individuals from Siberia, Ural mountains and Eastern Europe shows (as in the previous studies2, 3) a well-resolved bipartite distribution of haplotypes with separate Siberian and European branches, N1b-A and N1b-E, respectively (Figure 1). Previous studies have shown that South Siberian subcluster, N1b-A, may have originated first, later giving rise to the derived Northwest Siberian/Uralic/Northeast European subcluster, N1b-E.2, 3 However, new data presented here do not allow resolving the problem of geographic origin of hg N1b ancestor because the putative ancestral N1b haplotype (indicated by a star in Figure 1) appears to be equally widespread both in South Siberia (among Khakassians, Altaians, Mongolians, Tofalars, Evenks and Shors) and in Northwest Siberia (among Khants and Mansi). It is noteworthy, however, that earlier haplotype preceding subcluster N1b-E in the network is the haplotype revealed in Khants, pointing to the possibility of Northwest Siberian origin of the N1b-E subcluster.

Figure 1
figure 1

Median-joining network of hg N1b based on 11 STR loci (DYS19, DYS385a,b, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438 and DYS439) constructed using the Network 4.5.1.0. (www.fluxus-engineering.com)6 Presumed founder (and median) haplotype with allelic structure 14-12,13-13-16-23-10-14-13-14-10-10 for the aforementioned loci is indicated by a star. Circles represent STR haplotypes with area proportional to frequencies, and colors indicate the region of origin. South Siberian haplotypes (Tuvinian, Buryat, Mongolian, Altaian, Tofalar, Khakassian, Shor, Kalmyk and Evenk) are shown in black, Northwest Siberian haplotypes (Khants and Mansi) are shown in gray, whereas Uralic and Eastern European (Komi, Tatar, Mari, Vepsa and Russian) haplotypes are shown in white.

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According to our data, the age of STR variation within hg N1b as a whole is about 12 ky (12.1±4.4 ky). This age was estimated as the average squared difference in the number of repeats between all the current chromosomes and the founder haplotype, averaged over microsatellite loci and divided by the effective mutation rate of 0.00069 per locus per 25 years.7 We used the median haplotypes (formed by the median values of the repeat scores at each microsatellite locus within each hg) as the founding ones.8 The age of subcluster N1b-A in Siberian and Uralic populations is 4.2±1.1 ky, with the age prevailing in South Siberia in comparison with Northwest Siberia and Urals (4.8±1.7 vs 3.1±0.9 ky, respectively). However, the age of subcluster N1b-E in Northwest Siberian, Uralic and Northeast European Russian populations is much higher, being equal to 6.8±2.6 ky. Subcluster N1b-E differs sharply from N1b-A in its median repeat scores at four loci (DYS19, DYS385a,b, DYS389II and DYS392), thus suggesting that N1b-E chromosomes descended from single founders with multiple jumps at several loci, thus causing a possible shift in statistical estimates that assumes a step-wise mutation model.2

A possible scenario explaining the phylogeographic pattern of hg N1b is that the subclusters N1b-A and N1b-E might have diverged from a common ancestor anywhere in Siberia approximately 15 ky ago (with upper bound of divergence time, TD, between these subclusters estimated (according to Zhivotovsky9) as 14.7±5.9 ky). According to STR variation, expansion of Northwest Siberian/Uralic/Northeast European branch, N1b-E, may have occurred approximately 7 kya and the expansion of South Siberian branch N1b-A about 5 kya. Divergence time between South Siberian and Northwest Siberian/Uralic N1b-A haplotypes is 4 ky (TD=4.0±1.0 ky), so this suggests that expansion of N1b-A lineages in Northwest Siberia and Urals (about 3 kya) might have occurred right after their migrations from South Siberia. Future studies of Y-chromosome variation using a combined STR-SNP approach may enable a better definition of geographic origin of N1b-P43 mutation.