Analisi di un isolato sardo tramite il cromosoma Y: il caso Desulo

The Sardinian population is often analyzed in human genetic investigation because it shows a genetic peculiarity when compared with other European populations (Calò et al. 2013, 2012; Calò e Vona 2005; Capocasa et al. 2014; Cappello et al. 1996; Francalacci et al. 2003, 2013; Robledo et al. 2009; Vona 1995). Moreover, it was observed a high internal heterogeneity probably due to founders effects, isolation and bottleneck that occurred several times during Sardinia history. In this work I have analyzed the population of Desulo: a small village, located in the archaic zone of Sardinia (Vona 1995), that showed high level of endogamy (91.36%) and consanguinity (26.27%) between 1800 and 1974 (Sanna et al., 2004). The village of Desulo was composed until the 1920 by three separated neighborhoods: Issiria, Asuai and Ovolaccio, that subsisted as three independent units. Moreover, Desulo’s shepherds practiced transhumance towards the Sulcis Sardinian area. Hence, I wanted to test the level of population differentiation from different point of view: performing a comparison with other Sardinian populations, researching the presence of Desulo internal micro differentiation due to his subdivision in neighborhoods, and comparing it with other Mediterranean population. To perform this study 17 Y-STRs were analyzed: DYS19, DYS385 a/b, DYS389І/ІІ, DYS390, DYS391, DYS392, DYS393, DYS438, DYS439, DYS437, DYS448, DYS456, DYS458, DYS635, and YGATAH4. It was noteworthy the detection of the non consensus allele 18.2 in the locus DYS458. This frequencies is extremely low in the Caucasian and Italian populations (0.00317 and 0.014 respectively) but in Sardinian population it reaches the 0.1 % , furthermore all individuals carrying this allele belong to the haplogroup J1, confirming that the non consensus allele 18.2 can be used to discriminate the J1 haplogroup as suggested in previous studies (Alves et al. 2007b; Ghiani et al. 2009). Sardinia population, when compared with Mediterranean through Principal Component Analysis (PCA), resulted located in a separated cluster, also far from the Italian populations. However, this work shows an elevated internal heterogeneity of Sardinians: in fact performing a PCA with only Sardinian population, the formation of two clusters can been seen: one including North Sardinia and Benetutti, and the other one Sulcis and Central Sardinia. Instead, Carloforte and Desulo appear isolated. The latter is located very distant from Sulcis population, suggesting that despite the practice of transhumance, the two populations do not genetically interbred. The most frequent observed haplogroup is I2a1a determined by the M26 mutation, which reached the frequencies of 48% in the population of Desulo while in European population in extremely rare (<5%) (Ghiani et al. 2009). This high frequency can be due to founder effect occurred during the Paleolithic colonization of the Sardinia island (Contu et al. 2008; Francalacci et al. 2013; Varesi et al. 2000). For this reason it was chosen to study in deep the I2a1a subclades. All individuals carrying the mutation M26 always have the L160 mutation (haplogroup I2a1a1). The frequency of analyzed mutations (PF4124, 18866539, PF4258, PF4461, 21841733 e M161), determining the different subclades, varies significantly in the Sardinian population. This suggest that the sublclades variability of I2a1a haplogrup can be also due to genetics drift phenomena as founders effect and bottleneck and have remained in these areas through isolation. The isolation effect is also found at the micro geographic level in the village of Desulo. In fact, through the comparison with haplotipic data, the Issiria and Asuai districts appear differentiated, while Ovolaccio, the central district, seems to homogenate with the neighboring districts. In conclusion, when Sardinia is compared with Mediterranean populations it appears homogeneous, but if we are going to observe in detail only Sardinian population notice a large internal heterogeneity, detectable even at micro geographic level as in the case of the village of Desulo. For this reason it would be important to create, both for forensic and population genetics purposes, a database in which are recorded the different haplotypes detected in the Sardinian population. Moreover, with this study it was possible to clarify some doubt on the genetic Sardinian heterogeneity, but unfortunately exclusively inherent in the male line; therefore, it would be desirable to continue this study analyzing the mitochondrial DNA to see if the results obtained on the male line are also overlapping on the female line.