The use of surname and Y-chromocome analyses for reconstructing past population structures: the test case of Sardinia

The male specific region of the Y chromosome is uniparentally transmitted. It escapes recombination and its evolution is only due to the sequential accumulation of new mutations along radiating paternal lineages. Due to this process, which occurred mainly during and after the process of human colonization and diffusion into the different geographic region, the present Y-chromosome sequence variation represents a unique record of the biological history of our species and modern populations. Its analysis allows the identification of ancestral and founder haplotypes, the detection of ancient migration routes and the estimation of migration times. However, this analysis is sometimes undermined by recent migrations which became more and more important also for “isolated” populations, weakening the boundaries of genetic isolates by making uniform the distribution of genetic markers. A solution for this problem is represented by the reconstruction of the ancient isolates starting from the present data by using the information obtained from the surname analysis. With the aim of investigating the peopling of Sardinia and the aspects of its human Y-chromosome contemporary variation that can be ascribed to primary colonization, Neolithic dispersals or more recent events of gene flow, we have analyzed in detail the Y chromosome haplogroup distributions in a wide sample (more than 500 Y chromosomes) whose surname origin could be attributed specifically to one of the different Sardinian linguistic zones (Contini et al., 1989, Piazza et al. 1987). In addition, in order to evaluate the divergence of the different haplogroups observed in the island, and therefore their coalescent time, a set of 12 STR loci was examined. On the whole, by the comparison of 11 regions representative of ancient Sardinian isolates, a significant differentiation has been confirmed for the central eastern area of the island, in agreement with historical and linguistic data that indicate this region as the “archaic”zone. This is due to a lower incidence of haplogroups arrived in Europe during the Neolithic and post Neolithic times (Cruciani et al. 2004, Semino et et al. 2004), but mainly to a significative higher frequency of the Paleolithic haplogroup I-M26.