Characterization of Novel Mini STR Loci to Aid the Analysis of Degraded DNA Evidence in Sri Lankan Forensic Casework

Abstract

Miniaturized Short Tandem Repeat (miniSTR) markers have become increasingly useful in the analysis of degraded DNA specimens from mass disaster or forensic evidence during the past few years. Improved success of these markers are based on theirability to generate reduced sized fragments in Polymerase Chain Reaction (PCR) .Tropical climatic conditions present in Sri Lanka promote rapid DNA degradation in biological samples shed to a crime scene by perpetrator/s. Thus, obtaining a meaningful DNA profile using conventional analysis techniques under such circumstances is a challenge and often results in failed DNA analysis and result interpretation. This study screened literature for a new set of Mini STR loci that can generate reduced sized PCR products to aid in the analysis of degraded DNA evidence in Sri Lanka. New PCR primers for the novel STR loci D4S2632, D6S2436and D19S589 were designed. Maximum length of amplified fragments for theminiSTR loci D6S2436 , D19S589 was found to be less than 95 bp and 124 bp, respectively, whileD4S2632 extended to 180 bp. Allele frequency database for these mini STR loci was established by analyzing blood samples from443 unrelated individuals comprising Sinhalese, Sri Lankan Tamils and Sri Lankan Moors. Forensically important parameters i.e. polymorphic information content (PIC), heterozygosity (OH) and typical paternity index (PI) were determined. D4S2632, D6S2436and D19S589 showed a relatively high degree of polymorphism with observed heterozygosities>0.7 for the three ethnic groups analyzed. Two of the three mini-STR loci did not show any departure from the Hardy–Weinberg equilibrium for all the three populations tested whereas D4S2632 conformed to HW expectations only after the application of a Bonferroni correction. The population genetic evaluation on novel mini-STR loci for the Sri Lankan population confirmed their potential use as additional STR loci to provide greater discrimination for the analysis of highly degraded DNA evidence in Sri Lanka.