Extracting evidence from forensic DNA analyses: future molecular biology directions

Abstract

Molecular biology tools have enhanced the capability of the forensic scientist to characterize biological evidence to the point where it is feasible to analyze minute samples and achieve high levels of individualization. Even with the forensic DNA field's maturity, there still are a number of areas where improvements can be made. These include: enabling the typing of samples of limited quantity and quality; using genetic information and novel markers to provide investigative leads; enhancing automation with robotics, different chemistries, and better software tools; employing alternate platforms for typing DNA samples; developing integrated microfluidic/microfabrication devices to process DNA samples with higher throughput, faster turnaround times, lower risk of contamination, reduced labor, and less consumption of evidentiary samples; and exploiting high-throughput sequencing, particularly for attribution in microbial forensics cases. Knowledge gaps and new directions have been identified where molecular biology will likely guide the field of forensics. This review aims to provide a roadmap to guide those interested in contributing to the further development of forensic genetics.

Forensic Genetics and Genotyping

“…Nowadays, optimal amount of DNA is well defined and typically ranges from 100-200 pg to 2-3ng (1 ng is considered the optimum amount for most commercial kits) (27,28). The quantity of DNA is different in different biological samples (Table 1).…”

“…A sample may also be contaminated after it is collected from the crime scene and comes from the investigating officers, laboratory technicians and laboratory plastic ware. The issue of contamination is overcome by forming dedicated, specialized laboratories and by implementing protocols to reduce the risk of intra-laboratory contamination (28).…”

“…The small amplicon size of STRs (typically ranging from 100 to 500 bps in length) makes them suitable for the analysis of degraded DNA samples (2,9,27,36,38,39). The STR loci are currently the most informative genetic markers for identity testing (3,4,28,38). For example, the identity of the murdered Romanov family was confirmed using DNA extracted from bone fragments and amplified for 5 STR loci (HUMTH01, HUMVWA31, HUMF13A1, HUMFES/FPS, and HUMACTPB2), and amelogenin (40).…”

“…old bones, hair shafts) and minute amounts of cells occasionally lead to the elimination of single or, in the worst case, all alleles (2). In this case STR typing can be improved by moving the PCR primers closer to the STR repeat region, which reduces sizes of product while retaining the same information (3,28,36,41). Thus, STR products reduced in lengths are marked as mini STR and if they are smaller than some of the fragmented DNA template molecules, genetic characterization of the sample may then be possible (28,36).…”

“…In this case STR typing can be improved by moving the PCR primers closer to the STR repeat region, which reduces sizes of product while retaining the same information (3,28,36,41). Thus, STR products reduced in lengths are marked as mini STR and if they are smaller than some of the fragmented DNA template molecules, genetic characterization of the sample may then be possible (28,36). Butler have shown that the utility of these mini-STR assays has been confirmed in studies involving degraded bone samples and aged blood and saliva stains (36).…”