Forensic Science International: Genetics

X chromosome short-tandem repeats (X-STR) assays are helpful in complex kinship testing cases where autosomal and Y chromosome analyses convey little information. Their application has distinct advantages in mother-son and father-daughter kinship testing. Paternal relatives can be tested even in cases of deficiency paternity [1]. The purpose of this study was to create an allele frequency database for a southeast population in Spain and forensic efficiency parameters using X-linked chromosome STR markers [2]. This is the first report regarding the ten panel of X-linked chromosome markers developed by the Spanish and Portuguese Speaking Working Group of the International Society for Forensic Genetics (GHEP-ISFG) applied to the characterization of a southern population of the Iberian Peninsula. The Region of Murcia is located in the southeast coast of Spain within the Spanish Levant. The Spanish Levant is the collective name for four Mediterranean provinces on the Mediterranean coast. A sample of 172 unrelated individuals was selected for this study form the Murcia Twin Registry (MTR) database at the University of Murcia [3]. All the donors chosen for this study are residents of the Region of Murcia. Peripheral blood samples were collected and provided by the MTR following ethical requirements stipulated in governing laws [4,5]. Samples were extracted following standardized protocols at the National DNA Bank from the University of Salamanca. DNA quantitation was conducted at the BIOMICs Research Group from the University of the Basque Country using Quant-iT PicoGreen dsDNA Assay Kit (Invitrogen, Carlsbad, California) on a DTX880 Multimode Detector (Beckman Coulter, Fullerton, California). STR amplification and fragment analysis were performed as described in [6]. Statistical analyses calculated were performed using Arlequin software v3.5 [7] included: allele frequency, observed heterozygosity and Hardy–Weinberg equilibrium. Forensic efficiency parameters included: power of discrimination for females and males and probability of exclusion of paternity [8] for duos and trios. Pairwise genetic distances (Fst) were calculated with the same software using available population databases for the same X-STR markers. Pairwise genetic distances were used to construct an unrooted neighbor-joining tree using TreeFit [9] and visualized on TreeView [10]. Allele frequency and forensic efficiency parameters (Supplementary Table 1) were obtained for a total of 344 X-chromosomes. Deviations from Hardy–Weinberg equilibrium were not observed at any locus. Acceptable levels of power of discrimination and mean exclusion chance were determined. The most polymorphic locus was DXS6789. The highest power of discrimination was