Recent Male-Mediated Gene Flow over a Linguistic Barrier in Iberia, Suggested by Analysis of a Y-Chromosomal DNA Polymorphism

Abstract

We have examined the worldwide distribution of a Y-chromosomal base-substitution polymorphism, the T/C transition at SRY-2627, where the T allele defines haplogroup 22; sequencing of primate homologues shows that the ancestral state cannot be determined unambiguously but is probably the C allele. Of 1,191 human Y chromosomes analyzed, 33 belong to haplogroup 22. Twenty-nine come from Iberia, and the highest frequencies are in Basques (11%; n=117) and Catalans (22%; n=32). Microsatellite and minisatellite (MSY1) diversity analysis shows that non-Iberian haplogroup-22 chromosomes are not significantly different from Iberian ones. The simplest interpretation of these data is that haplogroup 22 arose in Iberia and that non-Iberian cases reflect Iberian emigrants. Several different methods were used to date the origin of the polymorphism: microsatellite data gave ages of 1,650, 2,700, 3,100, or 3,450 years, and MSY1 gave ages of 1,000, 2,300, or 2,650 years, although 95% confidence intervals on all of these figures are wide. The age of the split between Basque and Catalan haplogroup-22 chromosomes was calculated as only 20% of the age of the lineage as a whole. This study thus provides evidence for direct or indirect gene flow over the substantial linguistic barrier between the Indo-European and non-Indo-European-speaking populations of the Catalans and the Basques, during the past few thousand years.

The place of the Basques in the European Y-chromosome diversity landscape

“…There is some evidence of a short-range outward flow of Basque Y chromosomes, as the presence of R1b3d-M153 chromosomes in Iberia suggests. This finding is in agreement with previous data, 24 which provided more evidence for such gene flow between Basques and surrounding populations on the basis of haplogroup R1b3f-SRY2627. However, in agreement with additional data, 33 our data do not show any signs of long range diffusion of Basque Y-chromosome haplogroups into North Europe associated to the retreat of the last Glacial Maximum, as has been suggested for mitochondrial DNA.…”

“…This haplogroup is considered to be of Iberian origin as the highest frequencies and diversities for R1b3f-SRY2627 have been described in the Mediterranean area of the Iberian Peninsula. 24,25 The existence of a minor NW African male component (1.2%) in Basques is confirmed by the presence of the African lineages E3*-P2 and E3b2-M81. The latter is the most widespread haplogroup of the E cluster in Iberia, reaching its highest frequencies both in southern and northern parts of the Iberian Peninsula.…”

Human Y-chromosome variation in the Western Mediterranean area: implications for the peopling of the region

“…Consistent with previous analyses, HG22 was observed in Spain and surrounding regions. However, the postulated recent Iberian origin of this haplogroup [39] appears to be in contrast with its finding in our Russian sample (8%). Finally, the sub-Saharan-specific haplogroups 7.1, 7.2, 21, and 8 [4,18] were very uncommon and found only in six Berbers, one Arab, one Bedouin, three Palestinians, and seven Sardinians, which indicates that male-mediated gene flow across the Sahara has been very low both in historic and prehistoric times.…”

Using mitochondrial DNA to test the hypothesis of a European post-glacial human recolonization from the Franco-Cantabrian refuge

“…Interestingly, the latter lineage belongs to the phylogenetically older HV4a1 European clade that may have expanded around 9.7 ± 0.2 ky. The Y-chromosome counterparts for these maternal expansions in Iberia could be the R-M153 and the R-SRY2627 subclades (Hurles et al, 1999;Bosch et al, 2001). Both were recently detected in the Spanish Pyrenees and updated ages of 8.4 ± 2.7 ky for the former and 7.4 ± 1.5 ky for the latter were estimated (Lopez-Parra et al, 2009).…”