European Roma groups show complex West Eurasian admixture footprints and a common South Asian genetic origin

Abstract

The Roma population is the largest transnational ethnic minority in Europe, characterized by a linguistic, cultural and historical heterogeneity. Comparative linguistics and genetic studies have placed the origin of European Roma in the Northwest of India. After their migration across Persia, they entered into the Balkan Peninsula, from where they spread into Europe, arriving in the Iberian Peninsula in the 15th century. Their particular demographic history has genetic implications linked to rare and common diseases. However, the South Asian source of the proto-Roma remains still untargeted and the West Eurasian Roma component has not been yet deeply characterized. Here, in order to describe both the South Asian and West Eurasian ancestries, we analyze previously published genome-wide data of 152 European Roma and 34 new Iberian Roma samples at a fine-scale and haplotype-based level, with special focus on the Iberian Roma genetic substructure. Our results suggest that the putative origin of the proto-Roma involves a Punjabi group with low levels of West Eurasian ancestry. In addition, we have identified a complex West Eurasian component (around 65%) in the Roma, as a result of the admixture events occurred with non-proto-Roma populations between 1270-1580. Particularly, we have detected the Balkan genetic footprint in all European Roma, and the Baltic and Iberian components in the Northern and Western Roma groups, respectively. Finally, our results show genetic substructure within the Iberian Roma, with different levels of West Eurasian admixture, as a result of the complex historical events occurred in the Peninsula.

Fig 1. European Roma substructure (Dataset1).

(A) European Roma fineSTRUCTURE dendrogam showing the 10 European Roma clusters. (B) European Roma sample location and sample size (pie charts are colored according to the clusters in A).

Fig 2. West Eurasian and South Asian ancestry of the European Roma (Dataset1) from GLOBETROTTER results.

Pie charts on the map show the geographic location of the donor populations. Grey diamonds display those samples that do not contribute to the Roma ancestry. For each Roma cluster, the major source (West Eurasian like) and minor source (South Asian like) are shown: the proportion (in percentage) of each source and a horizontal bar with the proportions of the donor populations in each source. Only donor groups that contribute a minimum of 3% to the Roma genomes are shown. 1000G population labels are used in the map for ITU (Indian Telugu from the UK), STU (Sri Lankan Tamil from the UK), BEB (Bengali from Bangladesh), PJL (Punjabi from Lahore, Pakistan).

Fig 3. West Eurasian ancestry of the Iberian Roma (Dataset2).

Kriging model of the spatial distribution of the major source donor proportion inferred with GLOBETROTTER, reflecting the West Eurasian ancestry proportions in each Roma group (A-D).