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The mtDNA X2a Enigima

MtDNA haplogroups [Hgs] X1 and X2 diverged from macro-Hg N.Hg X1 is largely restricted to the Near East,North and East Africa.Unlike many mtDNa Hgs,which tend to have a more regional distribution.Hg X2 is widely dispersed throughout Eurasia and North America. Expansion times for X2,which are based on HVS-1 and coding region variation,are 17.9+/-2.9 Ka and 21.6+/-4.0Ka respectively.The tenuous,olderHVS-1 estimation for Hg X1 is 42.9+/-18.1 Ka.Hg X2 has 8 sub-clades [X2a-X2h],which are generally distributed over wide areas in relatively low frequencies.Dispersal “may” have commenced in the Near East.Ca one-third of the European Hg X sequences belong to sub-clades X2b and X2c.Southern European populations have higher X2 components than NE or northern EuropeansHg X2 is relatively rare among most eastern European mtDNA samples, [K Tambets,2004].The remains of a ca 1000 ADE Viking yielded sub-clade X2c [L Melchior,2008].

The Druze,a minority group in the Near East [eg: the Galilee Heights],harbour a frequency of ca 16% Hg X1.In the Peq’in on the Galilee Heights 6 of 17 specimens belonged to four distinct lineages of Hg X [X1a,X1b,X2e,and X2*],with a combined diversity of 0.667+/-0.02.A comparison of the Druze, Turkish and Egyptian Hg X sequences identified different lineages and coalescence times.The Druze have low migration rates,when compared to proximal populations,which could infer that the Druze are a Hg X refugium.The combination of a large number of X lineages and a significant Hg X component among the Druze suggests descent from an ancestral population,which probably had a higher representation of mtDNA Hg X [L Shlush,2008].It should be noted that Hg X sequences can not be confidently identified solely on variations in the hypervariable regional 1 [HSV-1] portion of the sequence.The minimal requirement is HVS-11.If the Hg has not been previously detected in a region,definitive coding mutations are required [G Horvat,2010].

Among Moroccan Jewish people the eight specimens,which were designated as X2b1,shared the identical control region haplotype 16183C-16189-16223-16248-16278-16519-73-153-195-225-226-263.The substitutions at nps 1555,2308 and 8814 have not been identified among existing X2 publications.The lineage was introduced to Morocco from the Near East [possibly via Iberia?].Tunisia and Libyan Jewish people share variants of the X2e1a1a lineage, [eg:Tunisia 39.8%].The coding region mutation 9380 is shared with samples from the Near East and Africa,but not with Europe [D Behar,2008].Analysis of 123 Turkish specimens indicated that 5.7% belonged to sub-clade x2g [16183C,16189,16278,16519,73,195,225,263,ibid].

The 8 sub-clades of X2 generally share transitions at Nucleotide positions [np] 195 and 1719.However transition 1719 is absent in one Georgian and two Lebanese samples [an early X2 branch or a np revision?].Hg X2 has an extensive low frequency distribution,which includes Lebanese 5.8%,Cypriots 6.7%,Druze and Orkney Islanders 7.2%.The latter have low haplotype diversities [0.4:0.473],which might be due to genetic drift or founder events.The X2e and X2f lineages constitute ca 88% of the southern Caucasus X sequences,which could be associated with post Younger Dryas population movements.Hg X distributions vary appreciably between the north [Nogays 4.2%;Kabardine 6.2%] and south Caucasus [Georgians 7.6%;Azers 4.2%].X2e,which is defined by the synomymous substitution at 15130 is present among the Altaian samples,that do not harbour any nucleotide differences between nps 16093 and 16365 [M Reida,2003].

The X2e mtDNA samples for 2 Altaians-Kizhi,1 Teleut and 1 Burgat were completely sampled and compared with a Caucasian specimen.The maximum parsimony tree revealed that the south Siberian X2e forms a separate cluster,which id defined by the coding region mutations 3948 and 13327,with two individuals sharing a coding region mutation at position 7853.A mutation at positon 3948 is present in a Georgian with a 3944 taq I variant It varies from the X2e root by 3 coding and 2 control region transitions.This divergence suggests that X2 was in Siberia ca 13.4+/-3.7Ka [M Derenko,2010].

G Derenko [2001] screened 793 native Siberians for Hg X,which was only detected in the Altaian samples.They had the 215G variant,that is not present among native North Americans and western Europeans.In a another study the Evenk,who live in the central Siberian Basin to the NE,yielded one X2b and another X2* samples,which do not appear to relate to the North American sub-cladeX2a [frequency ca 2%].Derenko postulated that the Altaian X2e occupies a position between European and North American mtDNA Hg X lineages.

MtDNA samples were obtained from 58 Daheyan villagers in the central Tarim Basin of China.Their language belongs to the Altaic linguistic family.Five Hg X specimens [frequency,8.6%] are characterized by 16145,16179,16183C,16189 and 16344 with one sample that included 16228.There is not sufficient data to identify a specific X2 lineage,but the five individuals do not appear to belong to X2e and they do not have the X2a specific 16213 [Yinqui Cui,2010].The Xiaohe cemetery in the Taklama Desert of NW China contains human remains that date as early as 2040 BCE +/-40a,cal. Reliable mtDNA data was extracted from the teeth of 20 skeletons.None of the specimens harboured Hg X.

The North American sub-clade X2a usually has C-T transitions np 16278 and np 16223,with the presence of DdeI sites np 1715 and np 10394.X2b varies from all its sister lineages [X2b-h] in Eurasia and Africa..To date Hg X has not been identified among indigenous Australians.”Uncontaminated” mtDNA was extracted from a ca 610 ADE human tooth at the Vantage site on the Columbia River in Washington State.R Malhi [2001] reported that the sample had the HVS 1 control region markers ;transition at np 16189,16223,and 16278 and the Acc I restriction site 14465 with G-A transition at np 16213,that is specific to X2a.The Vantage specimen is the oldest human in North America to test for X2a.It predates the Norse settlement in Newfoundland,Canada.However it does not predate the “possible speculative” arrival of a Phoenician or Carthagian woman with Hg X on board a vessel that could have been accidently blown across the Atlantic Ocean in a storm.

Kemp [2010] identified 7 Jemes individuals from New Mexico,who shared X2a1a1 genes and who probably had an affinity with the Sioux/Cheyenne.With the exception of one Ojibwa sample all of the Hg X specimens analysed by U Perago [2009] have the coding motif 8913-12397-14302.The anomalous Ojibwa did not cluster with any known X2a branches in North America or sister sub-clades in Eurasia.It “could” be another very rare founder.Private control region mutations distinguish two internal X2a branches ,which are X2a1 [143-16093] and X2a2 [225-16254C].X2a1 tends to be concentrated in the Great Lakes and Great Plains region X2a2 is less common [X2a1,19;X2a2,3; X2/,1].Some western fringe X2a specimens [eg:Nuu-Chah-Nuth,Yakima] lack characteristic X2a1 and X2a2 mutations [Ibid].

The current North American distribution of X2a tends to be concentrated in the vicinity of the Great Lakes/Great Plains with frequencies as high as 25% among some Algonquian people [eg:Ojibwa] with diminishing clines to the west and south.Frequency estimates range from Sioux ca 15%,Nuu-Chah-Nuth ca 13.5%,Navajo ca 6.5%,and Yakuma ca 4.8% [M Brown,1998].There are a few single or very frequency occurrences of X2a lineages  distal to the “Ojibwa core”.One X2a individual was identified among the Shuswap in the Caribou country of British Columbia and 5 0f 63 [7.9%] Nuu-Chah-Nuth samples off the west coast of British Columbia are probably X2a [there is not sufficient definitive data to substantiate this premise].The above tend to support the theory that X2a was introduced to North America from NE Siberia and that a number of intermediate Hg X lineages have been lost.A Nonosabasat sample from Newfoundland,eastern Canada,had X2a[10693C,16189C, 16213A,16223T,!6278T].A number of single occurrences have been reported from the Gaspe Peninsula,Quebec Province,but the data has not been sighted.G Horvati [2011] stated that X2a was identified in 3 of 6 MicMac sequences.

The dearth of indigenous mtDNA samples from the Maritime Provines of Canada,Quebec and British Columbia severely detract from endeavours to reconstruct the migration paths of the initial X2a colonists to North America.Consequently there has been a significant degree of speculation about the entry point to North America and the coalescence dates of X2a.Its apparent,current concentration in the Great Lakes/Great Plains region is an anomaly,which can not be confidently reconciled with an Alaskan entry point.This genetic founding lineage was probably introduced to North America from NE Siberia after the glacial era,but the current dispersal pattern of X2a is not in total accord with this supposition.”If” the Ojibwa did move from Nova Scotia to the Great Lakes region ca 1400 ADE,the enigma  gains in complexity.

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