DNA transfer in forensic science: A review

Abstract

Understanding the variables impacting DNA transfer, persistence, prevalence and recovery (DNA-TPPR) has become increasingly relevant in investigations of criminal activities to provide opinion on how the DNA of a person of interest became present within the sample collected. This review considers our current knowledge regarding DNA-TPPR to assist casework investigations of criminal activities. There is a growing amount of information available on DNA-TPPR to inform the relative probabilities of the evidence given alternative scenarios relating to the presence or absence of DNA from a specific person in a collected sample of interest. This information should be used where relevant. However, far more research is still required to better understand the variables impacting DNA-TPPR and to generate more accurate probability estimates of generating particular types of profiles in more casework relevant situations. This review explores means of achieving this. It also notes the need for all those interacting with an item of interest to have an awareness of DNA transfer possibilities post criminal activity, to limit the risk of contamination or loss of DNA. Appropriately trained forensic practitioners are best placed to provide opinion and guidance on the interpretation of profiles at the activity level. However, those requested to provide expert opinion on DNA-related activity level issues are often insufficiently trained to do so. We advocate recognition of DNA activity associated expertise to be distinct from expertise associated with the identification of individuals. This is to be supported by dedicated training, competency testing, authorisation, and regular fit for purpose proficiency testing. The possibilities for experts to report on activity-related issues will increase as our knowledge increases through further research, access to relevant data is enhanced, and tools to assist interpretations are better exploited. Improvement opportunities will be achieved sooner, if more laboratories and agencies accept the need to invest in these aspects as well as the training of practitioners.

DNA detection of a temporary and original user of an office space

“…Trace DNA samples collected from items/surfaces known or assumed to have been touched by hands, or other bare skin areas, represent a large proportion of DNA samples analysed by laboratories in different jurisdictions to assist investigations of criminal activity. The success rates for this type of sample vary greatly [1][2][3] and are affected by factors such as the type of item/surface, who touched it, how it was touched, when it was touched and environmental conditions [4]. The knowledge of success rates from particular items/surfaces can assist with limiting and prioritising items/surfaces to target with the aim of detecting a person of interest, as well as reducing costs, managing stakeholder expectations, identifying improvement opportunities, and providing useful investigative information [5,6].…”

“…The use of DNA profiles from touched items/surfaces has also raised the need to acquire a good understanding of issues relating to DNA persistence and transfer [4,7]. Improved knowledge in this area will assist in addressing frequently posed questions regarding activities of interest, such as those relating to the probability of detecting the last person who touched an item/surface given a particular action and their relative proportion (if not a single source), within any mixed profiles generated from samples collected.…”

A multidisciplinary approach is mandatory to solve complex crimes: a case report

“…After the discovery of the golf club, further investigations were made, thanks to the two different types of genetic analysis. Touch DNA was obtained from the epithelial cells left on the handled object (van Oorschot et al 2019). The difficulty in the extraction of this type of DNA is due to its invisibility and to the fact that it is usually present in small quantities on these items (Verdon et al 2014b).…”

A Study of the Background Levels of Male DNA on Underpants Worn by Females

“…KEYWORDS: forensic science, background DNA, underpants, Y chromosome, short tandem repeats, DNA profiling, evaluation, sexual assault Often in criminal cases, the source of the DNA is not questioned, rather how the DNA came to be there, and its significance (1,2). When someone is accused of a crime they may legitimately set forth an alternative explanation for the presence of their DNA, to that proposed by the prosecution.…”

“…When someone is accused of a crime they may legitimately set forth an alternative explanation for the presence of their DNA, to that proposed by the prosecution. The question of significance has driven a multitude of studies in the area of DNA transfer and persistence (2)(3)(4)(5)(6)(7).…”