Abstract
The peculiar position of Sardinia in the Mediterranean sea has rendered its population an interesting biogeographical isolate. The aim of this study was to investigate the genetic population structure, as well as to estimate Runs of Homozygosity and regions under positive selection, using about 1.2 million single nucleotide polymorphisms genotyped in 1077 Sardinian individuals. Using four different methods - fixation index, inflation factor, principal component analysis and ancestry estimation - we were able to highlight, as expected for a genetic isolate, the high internal homogeneity of the island. Sardinians showed a higher percentage of genome covered by RoHs>0.5 Mb (FRoH%0.5) when compared to peninsular Italians, with the only exception of the area surrounding Alghero. We furthermore identified 9 genomic regions showing signs of positive selection and, we re-captured many previously inferred signals. Other regions harbor novel candidate genes for positive selection, like TMEM252, or regions containing long non coding RNA. With the present study we confirmed the high genetic homogeneity of Sardinia that may be explained by the shared ancestry combined with the action of evolutionary forces.
Highlights
Due to the geographic isolation of Sardinia in the Mediterranean sea, Sardinian population can be considered a genetic isolate
Much remains to be discovered about the genomic regions that were inherited from common ancestors, such as the short Runs of Homozygosity (RoHs), or the portions of the genome that have been selected by positive sweep
No sub-populations were apparently identified projecting the Sardinian samples onto a two-dimensional space using all autosomal markers (934,288 single nucleotide polymorphisms (SNPs)) within the linguistic macroareas (Figure 2A), or dividing the island in 3 geographic regions (Figure 2B)
Summary
Due to the geographic isolation of Sardinia in the Mediterranean sea, Sardinian population can be considered a genetic isolate. Faunal and floral endemism underline this peculiarity, which is reflected in the genetic and cultural structure of the human population. For such reasons, Sardinians have been object of numerous investigations in the fields of anthropology and population genetics [1,2,3,4]. Several studies have shown that the genome of current Sardinia inhabitants still contains some signatures of a long history of isolation. These features make this genetic isolate an ideal population for association studies [5,6,7]. Much remains to be discovered about the genomic regions that were inherited from common ancestors, such as the short Runs of Homozygosity (RoHs), or the portions of the genome that have been selected by positive sweep
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