Getting back to the point raised earlier about the rare 12-repeat allele at DYS392 by Semino et al...
It is interesting that both E-P2* and E-M35* and their derivatives, E-M78 and E-M123, exhibit in Ethiopians the 12-repeat allele at the DYS392 microsatellite locus, an allele scarcely seen (Y-Chromosome STR Database), especially in other haplogroups and other populations (A.S.S.-B., unpublished data).
In addition, the Ethiopian DYS392-12 allele is usually associated with the unusually short DYS19-11 allele, which is typical of this area. These findings are not easily explained. One possible scenario is that an ancient differentiation of the E-P2 haplogroup occurred in loco (East Africa). However, this also implies a low mutability of the associated microsatellite motif (DYS392-12/DYS19-11). Alternatively, the microsatellite motif may be due to homoplasy.The first scenario is more likely, since this unique microsatellite haplotype occurs in E-P2*, E-M35*, and E-M78 but is almost *absent in all other haplogroups and populations*.
In addition, the high stability of the DYS392 locus (Brinkmann et al. 1998; Nebel et al. 2001) and of the shorter alleles of DYS19 (Carvalho-Silva et al. 1999) has been reported elsewhere.
Moreover, the observation that the derivative E-M78 displays the DYS392-12/DYS19-11 haplotype suggests that it also arose in East Africa. This is illustrated by the microsatellite network (fig. 3, shaded area), which reveals that the Ethiopian branch harboring DYS392-12 is not shared with either Near Eastern or European populations. — Semino et al. Origin, Diffusion, and Differentiation of Y‐Chromosome Haplogroups E and J, 2004.
To which the present author responded...
The Ethiopian sample may not share the said allele with those populations mentioned, including the northwest African samples as far as I can tell, but it does share the said allele with the Senegalese sample [see fig. below], which would suggest that the Senegalese M78 derivative didn’t come from interaction with its northwest African neighbors; rather, they may well be relics of ancient migrations from east to west.
Cruciani et al. in their 2007 publication, Tracing human male movements in northern/eastern Africa and western Eurasia: new clues from Y-chromosomal haplogroups E-M78 and J-M12, had this to say about the 12-repeat allele in question:
“An eastern African origin for this haplogroup was hypothesized on the basis of the basis of the exclusive presence in that area of a putative ancestral 12-repeat at the DYS392 micro satellite , found in association with E-M78 chromosomes (Semino et al. 2004). North-eastern African populations were not represented in that study.
In order to test this hypothesis, we analyzed for DYS392 a geographically widespread subset of the E_M78 chromosomes here identified. We observed that the DYS392 12-repeat allele is associated with the majority of the chromosomes belonging to the north-eastern African E-V12* (15 out of 18) and to the eastern African E-V32 (21 out of 23), with about half (9 out of 21) of the E-V22 chromosomes (both in eastern and north-eastern Africa), with a few of the European E-V13 (2 out of 23) and with some north-African E-V65 (3 out of 16) chromosomes.
These findings show that the DYS392 12-repeat allele is common in different regions characterized by high frequencies of E-M78, and suggest that it was most likely generated by multiple mutation events occurring in different UEP-defined sub-haplogroups. Thus, the DYS392 allele distribution is not informative to infer the place of origin of E-M78 chromosomes.”
Cruciani et al. point out that Northeast Africa wasn't represented in the 2004 Semino et al. study, presumably to emphasize the point that its detection therein would have shown that the 12-repeat allele in question wasn't confined to sub-Saharan east Africa, particularly Ethiopia. It is certainly true that northeastern Africa was not represented, but in fact, a close examination of Semino et al.'s 2004 study, shows that the 12-repeat allele wasn't confined to sub-Saharan east Africa; it makes single or very low appearances in the "Near Eastern" and "European" samples, and interestingly none in north African [sans northeast Africa] samples.
Cruciani et al. on the other hand, did detect the 12-repeat allele in north African [sans northeast Africa], but still in relative low frequency (3 out of 16). The same applies to their findings in European samples, where it appears to be yet rarer than that of the north African samples. Considerable frequency is however noted in their northeast African sample, and consistently, in sub-Saharan east African samples. So, even going by Cruciani et al.'s findings, the greater distribution of the 12-repeat allele in eastern Africa in general, would argue for its introduction from eastern Africa.
Cruciani et al. reckon that simply because the 12-repeat allele is not confined to east Africa, it therefore doesn't allow one to infer the place of origin of E-M78 chromosomes. This ignores the point just made about its relatively rare occurrence outside of east Africa. Cruciani et al. reach this conclusion on the understanding that the 12-repeat allele's appearances in distinct sub-clades invokes homoplasy or parallel mutational events, and indeed, Semino et al. 2004 did not rule out that possibility, but unlike Cruciani et al. they took additional material into consideration:
—1) "It is interesting that both E-P2* and E-M35* and their derivatives, E-M78 and E-M123, exhibit in Ethiopians the 12-repeat allele at the DYS392 microsatellite locus, an allele scarcely seen..."
So while there is notable presence of 12-repeat allele bearing E-M78 chromosomes in northeast Africa as well, only in sub-Saharan east Africa does one come across not only considerable frequencies of E3-P2 [PN2 clade], but also the more immediate precursor of E-M78, i.e.—E-M35*, which bear this 12-repeat allele. As far as the present author can tell at this point, pending introduction to studies that suggest otherwise, the ensemble of at least three different PN2 macro-clade—including the ancestral ones—bearing the said 12-repeat allele, only occures in sub-Saharan east Africa. Case in point:
"...first scenario is more likely, since this unique microsatellite haplotype occurs in E-P2*, E-M35*, and E-M78 but is almost *absent in all other haplogroups and populations*."
—2) "One possible scenario is that an ancient differentiation of the E-P2 haplogroup occurred in loco (East Africa). However, this also implies a low mutability of the associated microsatellite motif (DYS392-12/DYS19-11)...
In addition, the high stability of the DYS392 locus (Brinkmann et al. 1998; Nebel et al. 2001) and of the shorter alleles of DYS19 (Carvalho-Silva et al. 1999) has been reported elsewhere."
So again, while not ruling out independent parallel microsatellite mutational events across different PN2 clades, the repeat occurrence of the 12-repeat allele across different PN2 clades, including the ancestral ones, coupled with the possibility of "low mutability", which translates into "high stability" of the locus in question, indicates that the 12 repeat could well have also been inherited from a precursor PN2 clade(s). If the latter is the case, certainly sub-Saharan East Africa as the likely place of origin for the allele, can be put forward as a strong argument. And in getting back to the appearance of this allele in sub-Saharan or Sahelian west Africa, in the Senegalese sample for instance, would tend to favor an east African origin at some point in history, rather than as a remnant of interactions with coastal northwest Africans, where the allele is rare, even going by Cruciani et al.'s findings.
Initially posted here:
