Genetic diversity of 12 X-chromosomal short tandem repeats in the Moroccan population

Exploring the Western Mediterranean through X-chromosome

In this study, we investigate the forensic and population genetics properties of 21 X-chromosome markers (9 X-Alu insertions and 12 X-STRs) in a dataset composed of 716 individuals from 11 Western Mediterranean populations. The high values of combined forensic parameters indicate that this 21 X-loci panel can complement autosomal or uniparental markers in kinship analysis and complex deficient paternity testing in the populations studied. Population analyses revealed a lower differentiation between Western Mediterranean human groups for X-STRs than for X-Alu insertion polymorphisms. Moreover, X-chromosome markers suggest a sex-biased migration rate, confirming the predominance of patrilocality in this area.

Allele and haplotype diversity of 12 X-STRs in Sardinia

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, and three isolates (Benetutti, Desulo, Carloforte). 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. The study confirms the presence of high levels and complex patterns of LD along the X chromosome in Sardinia, and provides population-specific haplotype data for biostatistical evaluation in kinship testing.

Analysis of 12 X-STR loci in the population of south Croatia

The aim of the study was to assess forensic pertinence of 12 short tandem repeats (STRs) on X-chromosome in south Croatia population. Investigator^® Argus X-12 kit was used to co-amplify 12 STR loci belonging to four linkage groups (LGs) on X-chromosome in 99 male and 98 female DNA samples of unrelated donors. PCR products were analyzed by capillary electrophoresis. Population genetic and forensic parameters were calculated by the Arlequin and POPTREE2 software, and an on-line tool available at ChrX-STR.org. Hardy-Weinberg equilibrium was confirmed for all X-STR markers in female samples. Biallelic patterns at DXS10079 locus were detected in four male samples. Polymorphism information content for the most (DXS10135) and the least (DXS8378) informative markers was 0.9212 and 0.6347, respectively. In both male and female samples, combined power of discrimination exceeded 0.999999999. As confirmed by linkage disequilibrium test, significant association of marker pair DXS10074-DXS10079 (P = 0.0004) within LG2 and marker pair DXS10101-DXS10103 (P = 0.0003) within LG3 was found only in male samples. Number of observed haplotypes in our sample pool amounted 3.01, 7.53, 5 and 3.25% of the number of possible haplotypes for LG1, LG2, LG3 and LG4, respectively. According to haplotype diversity value of 0.9981, LG1 was the most informative. In comparison of south Croatia with 26 world populations, pair-wise [Formula: see text] values increase in parallel with geographical distance. Overall statistical assessment confirmed suitability of Investigator^® Argus X-12 kit for forensic casework in both identification and familial testing in the population of south Croatia.

Genetic ancestry of a Moroccan population as inferred from autosomal STRs

Detecting population substructure and ancestry is a critical issue for both association studies of health behaviors and forensic genetics. Determining aspects of a population's genetic history as potential sources of substructure can aid in design of future genetic studies. Within this context, fifteen autosomal short tandem repeat (STR), were used to examine population genetic structure and hypotheses of the origin of the modern Moroccan population from individuals belonging to three different ethnical groups from Morocco (Arab, Berber and Sahrawi), by comparing their autosomal STR variation with that of neighboring and non-neighboring populations in North Africa, Europe and Middle East as well as proposed ancestral populations in Morocco (Berber). We report on the results that the gradient of North African ancestry accounts for previous observations of low levels of sharing with Near East and a substantially increased gene flow especially from Morocco and Spain.