HUMAN MITOCHONDRIAL-DNA VARIATION AND THE ORIGIN OF BASQUES

The hypervariable segment I of the control region of the mtDNA (positi ons 16024-16383) was PCR-amplified from mouth scrape and hairs and seq uenced in 45 unrelated individuals of pure matrilineal Basque descent. Twenty-seven different sequences were found, of which 21 are unique t o the Basques. The allelic partition observed, together with resamplin g experiments, suggested that much more variation remained to be disco vered. The mean pairwise difference in number of nucleotides between i ndividuals was 3.15, a very low value. Moreover, the number of steps f or the most parsimonious tree is very low compared to the number of di fferent sequences. Both findings suggest that the Basque population wa s founded by a few lineages that diverged in a short time span. The nu mber of nucleotide differences between individuals was shown not to be influenced by the distance between their birthplaces, thus validating the sampling strategy used a posteriori. The pairwise difference dist ribution agreed well with the three-parameter model proposed by Rogers & Harpending (1992). The parameter estimates found for the Basques im plied that a demographic expansion (or perhaps two, given the bimodal shape of the distribution) took place sometime between 14500 and 42000 sp which is in agreement with archaeological data. Our sample was com pared to other populations for which D-loop sequences were available t hrough the Nei & Miller (1900) distance. In a neighbour-joining tree, all the Caucasoid samples, including the Basques, appeared tightly clu stered, whereas African samples were the most distant to the Caucasoid s and also the most heterogeneous. Although classical markers, such as blood groups and protein polymorphisms, clearly separate the Basques (and the Sardinians) from other European populations, this distinctive ness was not found using D-loop sequences.