November 01, 2005

mtDNA of Latvians

Interesting new study on a Baltic-speaking population. From the conclusions:
Overall, the present study fills a gap which existed and shows that the maternal lineages of Baltic-speaking populations, Latvians and Lithuanians, and of their Slavonic- and Finno-Ugric-speaking neighbours, in particular Estonians, form a close cluster. This cluster also includes Germans, as well as Germanic-speaking Scandinavians, suggesting a recent shared maternal ancestry as well as pre-historic and historic time gene flows across linguistic borders. However, this maternal gene flow (migration of females) contrasts with an apparent lack of westward flow of hg N3 Y chromosomes (migration of males). The Baltic-speaking populations largely share a mosaic of frequencies that, in Europe, brings them together specifically with the Finnic-speaking populations, both those living in the Baltic area and those living in the Volga Basin. It remains to be seen whether rapidly advancing technologies for complete genome variation studies may in future reveal autosomal genes with a spread closely matching that of either of the contrasting haploid genetic systems of the Y chromosome and mtDNA.

Haplogroup frequencies in Latvians and others:

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The paper also mentions briefly some information about the age of haplogroup N3:
Meanwhile, it is interesting to note that the calculations of Kasperaviciuteet al. (2004) suggested very similar expansion times, around 7000 - 8000 BP, for the Lithuanian and Estonian hg N3 Y chromosomes, which are probably also applicable to Latvians. Therefore, it is indeed possible that the spread of hg N3 among the ancestral populations of Estonians, on the one hand, and the Baltic-speaking populations on the other, pre-date the advent of the Neolithic age in the East Baltic and may be part of the post-LGM re-colonisation of the region.
The authors refer to an article (Ann Hum Genet 68, 438-452) which gives estimates of the age of haplogroup N3:
The lower gene diversity and nearly star-like median joining network of Lithuanian HgN3 chromosomes suggests a bottleneck involving HgN3 chromosomes in Lithuania; therefore, a demographic analysis using a Bayesian-based coalescence approach was performed (Table 6). A signal of population growth was detected both in Lithuanians and Estonians (the Latvian sample was excluded from this analysis because of the small sample size), and also for the combined dataset, corrected for differences in sample sizes. The dates of the start of the population growth depended greatly on the mutation rate estimate used for calculations, and varied from ~1000 years (using the mutation rate obtained from father-son pairs (Kayser et al. 2000b)) to ~7-8000 years (using the phylogenetic mutation rate estimate (Zhivotovsky et al. 2004)). The true date probably lies in between these estimates. Interestingly, similar dates were obtained for HgR1a Lithuanian chromosomes and all Y chromosomes, indicating that population growth was characteristic for the whole population, while a reduction of diversity is seen only among HgN3 chromosomes.
Hence, the authors of the current paper arbitrarily picked the earliest date as supportive of their pre-Neolithic hypothesis, even though the data can't distinguish between Neolithic and pre-Neolithic. Moreover, even using the phylogenetic mutation rate, the confidence intervals are consistent with both the Paleolithic and Neolithic dates.

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This underscores the importance of appreciating the many factors which contribute to error in time estimates using molecular data on living populations.

Annals of Human Genetics
(Online early)

Mitochondrial DNA Portrait of Latvians: Towards the Understanding of the Genetic Structure of Baltic-Speaking Populations

L. Pliss et al.

Mitochondrial DNA (mtDNA) variation was investigated in a sample of 299 Latvians, a Baltic-speaking population from Eastern Europe. Sequencing of the first hypervariable segment (HVS-I) in combination with analysis of informative coding region markers revealed that the vast majority of observed mtDNAs belong to haplogroups (hgs) common to most European populations. Analysis of the spatial distribution of mtDNA haplotypes found in Latvians, as well as in Baltic-speaking populations in general, revealed that they share haplotypes with all neighbouring populations irrespective of their linguistic affiliation. Hence, the results of our mtDNA analysis show that the previously described sharp difference between the Y-chromosomal hg N3 distribution in the paternally inherited gene pool of Baltic-speaking populations and of other European Indo-European speakers does not have a corresponding maternal counterpart.


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