A Quantitative Study On Extraction Versus Direct Amplification Of Touch DNA Samples

Abstract

Touch DNA, also known as Trace DNA, is an important aspect of criminal investigations, as the perpetrator is unaware of the DNA they have left behind. While there are multiple ways to extract touch DNA, it has been established that direct amplification provides exemplary results. Direct Amplification is the process of analyzing the samples by amplifying them without extraction or quantitation. However, there is no measure on how much information direct amplification provides as opposed to other widely used methods including standard extraction procedures. This study aimed to look at the differences in information obtained when processing a touch DNA sample using standard extraction procedures versus a direct amplification approach. Understanding the scope of information collected by direct amplification versus standard extraction procedures can be used to facilitate new protocols for processing touch DNA. This study focused on collecting touch DNA samples from 20 volunteers and processing the DNA using two methods. In the first half of the study, half of the samples were extracted, quantified, and amplified using the InnoXtractTM, InnoQuantTM and InnoTyperTM kits, respectively, from InnoGenomics, LLC. The next part of the study included adding swabs to be directly amplified using the InnoTyperTM 21 kit. Rather than the standard extraction protocol, this method included placing the swab heads directly into the PCR tubes for amplification. Samples undergoing direct amplification are expected to show more information due to the fact that standard extraction protocols often result in loss of DNA. Data generated from capillary electrophoresis was compared by reviewing the allele peak heights. Samples exhibiting “real” and representative peaks were further reviewed to determine if the peaks were real or due to artifacts such as noise. The research findings may lead to revised protocols that can be applied to difficult sample types, such as touch DNA, which often result in partial DNA profiles that often contain very little information.