Forensic identification from human fingermarks using direct PCR to improve DNA recovery.

Author: Jennifer Templeton

  • Thesis download: available for open access on 6 Sep 2020.

Templeton, Jennifer, 2017 Forensic identification from human fingermarks using direct PCR to improve DNA recovery., Flinders University, School of Biological Sciences

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Abstract

My original contribution to knowledge is the application of direct PCR for sampling ‘touch’ DNA obtained from fingermarks for the purpose of human identification. DNA from fingermarks can be crucial evidence in forensic cases where partial or smudged prints are obtained and hence cannot be used for classical fingerprinting. Advances in technology have facilitated the typing and interpretation of trace or low-level DNA from fingermarks. It is well-known in forensic science that fingermark traces may possess limited DNA. The flow-on effect of this is that the DNA profiling of fingermarks often yields little or no information that can be used to assist forensic investigations. For samples such as fingermarks, every effort needs to be made to reduce processes that are wasteful of DNA so that the success rate for DNA profiling is maximised. Standard processing in most forensic laboratories involves the sample going through a DNA extraction step, which is known to lose high percentages of DNA. One possible workflow that removes the DNA extraction step involves placing the sample directly into the Polymerase Chain Reaction (PCR). This process is called ‘direct PCR’ and has shown to be successful in other forensic applications where traditional DNA profiling failed. This thesis examines the effectiveness of direct PCR to generate DNA profiles from fingermarks. Informative DNA profiles were obtained from swab fibres used to recover DNA from plastic, wood, glass and metal substrates. Further results highlight the potential for dusted fingerprints to be successfully profiled. A case report is included (see Chapter IV) demonstrating the application of the technique in real case work where DNA was recovered from a smudged fingermark on the surface of a drug seizure. Additionally, a mock case demonstration highlights that direct PCR can be used on samples subjected to environmental exposure. In this thesis, the quality of a DNA profile is assayed by the relative peak height of the alleles, associated artefacts, allele ‘drop-in’ and ‘drop-out’. In the first data chapter, a comparison to standard non-direct PCR was carried out (i.e. extraction followed by PCR). The data I obtained infer better quality STR-based DNA profiles recovered by direct PCR over conventional extraction. It was found that informative profiles can be generated from fingermarks left by an individual only 15 minutes after washing hands. The use of a detergent-based nylon flocked swab was trialled and resulted in improved quality of the DNA profiles obtained. The donors of the prints were able to be identified in a quicker time-frame than is currently possible with traditional methods that involve DNA extraction. Direct PCR reduces the opportunity for contamination by eliminating the multiple tube changes and additional steps required during an extraction. Consequently, there is a reduction in the cost of labour and reagents needed to process samples and a high through-put potential for case work exhibits. According to Forensic Science South Australia (FSSA), direct PCR is at times the only way to obtain a DNA profile from a crime scene exhibit. Ultimately, the work showed that direct PCR has a role to play in case work and proved to be reliable, robust and reproducible.

Keywords: touch DNA, STR, identification, forensic
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2017
School: School of Biological Sciences
Supervisor: Professor Adrian Linacre