March 17, 2013

Autosomal genetics of the Roma People

Some more information on the genetics of the Roma People.

Prija Moorjani et al., Reconstructing Roma History from Genome-Wide Data. PLoS ONE 2013. Open accessLINK [doi:10.1371/journal.pone.0058633]


The Roma people, living throughout Europe and West Asia, are a diverse population linked by the Romani language and culture. Previous linguistic and genetic studies have suggested that the Roma migrated into Europe from South Asia about 1,000–1,500 years ago. Genetic inferences about Roma history have mostly focused on the Y chromosome and mitochondrial DNA. To explore what additional information can be learned from genome-wide data, we analyzed data from six Roma groups that we genotyped at hundreds of thousands of single nucleotide polymorphisms (SNPs). We estimate that the Roma harbor about 80% West Eurasian ancestry–derived from a combination of European and South Asian sources–and that the date of admixture of South Asian and European ancestry was about 850 years before present. We provide evidence for Eastern Europe being a major source of European ancestry, and North-west India being a major source of the South Asian ancestry in the Roma. By computing allele sharing as a measure of linkage disequilibrium, we estimate that the migration of Roma out of the Indian subcontinent was accompanied by a severe founder event, which appears to have been followed by a major demographic expansion after the arrival in Europe.

The claim of "80%" West Eurasian ancestry seems quite exaggerated on light of the ADMIXTURE data, where at least 40% is clearly of South Asian origin (maybe somewhat more as NW South Asians display some West Eurasian admixture). I guess that they are just speculating on the ANI/ASI (North-South Indian) issue and attributing ANI to a West Eurasian gene pool, what is most confusing to say the least.

Figure 1. Relationship of Roma with other worldwide populations.
(click to expand)

It is true in any case that FST distances are significantly higher with Gujarati Indians (GIH) than with Europeans (CEU, TSI), the former at 0.026, while the latter at only 0.016.

Whatever the case I'd focus on the Fig 1(a) ADMIXTURE graph, because in the (b) one the appearance of European affinity among many South Asians (in my understanding, a 50,000 years-old affinity highlighted only for lack of sufficient K-depth, K=3 only!) is only a factor of confusion. Following this criterion, Roma appear to be some 60% West Eurasian and 40% NW Indian.

Something I really miss in this paper is a more detailed comparison not just with South Asians (more K-depth please!) but also with West Asians, totally absent from the study.

See also: Romani mtDNA

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