Recent male-mediated gene flow over a linguistic barrier in Iberia, suggested by analysis of a Y-chromosomal DNA polymorphism

We have examined the worldwide distribution of a Y-chromosomal base-substit ution polymorphism, the T/C transition at SRY-2627, where the T allele defi nes haplogroup 22; sequencing of primate homologues shows that the ancestra l state cannot be determined unambiguously but is probably the C allele. Of 1,191 human Y chromosomes analyzed, 33 belong to haplogroup 22. Twenty-nin e come from Iberia, and the highest frequencies are in Basques (11%; n = 11 7) and Catalans (22%; n = 32). Microsatellite and minisatellite (MSY1) dive rsity analysis shows that non-Iberian haplogroup-22 chromosomes are not sig nificantly different from Iberian ones. The simplest interpretation of thes e data is that haplogroup 22 arose in Iberia and that non-Iberian cases ref lect Iberian emigrants. Several different methods were used to date the ori gin of the polymorphism: microsatellite data gave ages of 1,650, 2,700, 3,1 00, or 3,450 years, and MSY1 gave ages of 1,000, 2,300, or 2,650 years, alt hough 95% confidence intervals on all of these figures are wide. The age of the split between Basque and Catalan haplogroup-22 chromosomes was calcula ted as only 20% of the age of the lineage as a whole. This study thus provi des evidence for direct or indirect gene flow over the substantial linguist ic barrier between the Indo-European and non-Indo-European-speaking populat ions of the Catalans and the Basques, during the past few thousand years.