Abstract
Diversity profile of 15 short tandem repeat (STR) loci was evaluated using AmpFISTR Identifier kit (Applied Biosystems) in DNA from 120 healthy native Qataris after informed consent. All the 16 markers (including the Amelogenin gender differenciator) were amplified by PCR using the commercially available ?Identifier primer set? in a multiplexed reaction. Size separation of the PCR products was carried out by electrophoresis on a 3100 genetic analyser (Applied Biosystems) including positive and negative controls as well the size standards. Allele identification and tabulation was performed using Genemapper v3.2 software. Statistical analyses including determination of the matching probability, power of discrimination (PD), polymorphism information content, power of paternity exclusion (PE), and typical paternity index were performed using the software PowerStats (Promega Corporation, Madison, Wisconsin). The discriminating power of a locus, which represents the probability that two randomly chosen subjects do not have the same genotype, was calculated as 1-Pi, and the combined discriminating power of the 15 loci as 1 - (? Pi), where Pi is the sum of the squares of frequencies of all genotypes at a given locus. The higher the discriminating power of a locus, the more efficient it is in discriminating between members of the population. The power of paternity exclusion, defined as the fraction of individuals who would not have the same DNA profile, was calculated from the following formula: PE=h2 (1- 2hH2), where h is heterozygote frequency and H is homozygote frequency. The higher the PE value, more the non-fathers are excluded. The combined power of paternity exclusion was calculated as 1 ? ?(1- PEi). The typical paternity index was calculated as (H+h)/2H. Overall genotype distribution adhered to expectations from Hardy-Weinberg equilibrium by three independent testings for all markers (0.00333). No significant linkage disequilibrium (LD) was noted between any pair of loci after Bonferroni correction (0.000476). We found that the most discriminating locus in the study population was D2S1338 (PD=0.969), while the least informative locus was TPOX (PD=0.821). Individual power of exclusion values ranged from 0.322 (TPOX) to 0.762 (FGA). They indicated low degrees of exclusionary power for the loci when used individually. However, combined power of discrimination and combined power of exclusion were both estimated to be greater than 0.9999 for the Qatar population sample, thereby demonstrating the forensic utility / individual identification of a multilocus-based analysis.