Variabilità allelica ed aplotipica degli X-STR in Sardegna

The analysis of clusters of tightly linked X-chromosome short tandem repeat (STR) markers can assist the interpretation of complex kinship cases. However, when linkage disequilibrium (LD) is present in the population of origin of tested individuals, haplotype rather than allele frequencies should be used in likelihood calculations. The diversity of twelve X-STRs arranged in four linkage groups (I: DXS10148-DXS10135-DXS8378; II: DXS7132-DXS10079-DXS10074; III: DXS10103-HPRTB-DXS10101; IV: DXS10146-DXS10134-DXS7423) was tested in a Sardinian population sample (n = 516) including three open populations from the Northern, Central and Southern part of the island, as well as geographic (Benetutti, Desulo) and linguistic (Carloforte) isolates. Evidence of LD was detected in Sardinia within each linkage group. Significant differences in haplotype and allele frequency distribution of X-STR markers was seen between isolates and open populations, which on the contrary appeared highly homogeneous. The percentage of Sardinian haplotypes previously unobserved in a similar dataset compiled for the Italian population was: 76.3% (linkage group I), 61.3% (linkage group II), 54.1% (linkage group III), 58.9% (linkage Group IV). Significant pairwise genetic differences were seen between mainland Italy, the three Sardinian isolates, and the open population of Southern Sardinia. Comparisons between Sardinians and other relevant populations from Europe, Northern Africa, and the Middle East highlight the outlier position of Sardinian geogrphic isolates within the Mediterranean genetic landscape, and support the hypothesis of sex-biased admixture in the Carloforte sample in agreement with previous studies of haploid markers (Y chromosomee, mitochondrial DNA). Finally, analysis of Sardinian full sibs and aunt ¿ niece pairs showed that use of non population-specific (Italian) haplotypic data in kinship calculations can lead to an > 103-fold overestimation of the weight of evidence.