Determination of shedder status: A comparison of two methods involving cell counting in fingerprints and the DNA analysis of handheld tubes

Peter Gill,Helen Johannessen,Ane Elida Fonneløp,Arne Roseth

doi:10.1016/j.fsigen.2021.102541

Peter Gill, Helen Johannessen + Show 2 more

Open Access

https://doi.org/10.1016/j.fsigen.2021.102541

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Abstract

The shedder status of an individual may be important to consider in the context of DNA transfer, persistence and recovery and in Bayesian networks where a person’s shedder status may have an impact on the outcome. In this study we compared two methods to determine shedder status: the handheld tube (HH) method and a fluorescent cell count (CC) method. A poor association was observed between the numbers of detected cells in a fingerprint using the CC method and the strength of the DNA result with the HH method. The 20 participants were classified into low (25%), medium (50%) and high (25%) shedders based on the HH method. While the low and high shedders showed a good consistency between the replicates, the medium shedders varied more and have to be considered more carefully as they may act as either a high or a low shedder in an event of DNA transfer.

Highlights

In court, expert witnesses are often asked to address questions that concern the activity which led to the deposition of a defendant’s DNA on an item or surface
A poor association was observed between the numbers of detected cells in a fingerprint using the cell count (CC) method and the strength of the DNA result with the handheld tube (HH) method
While the low and high shedders showed a good consistency between the replicates, the medium shedders varied more and have to be considered more carefully as they may act as either a high or a low shedder in an event of DNA transfer

Summary

Introduction

Expert witnesses are often asked to address questions that concern the activity which led to the deposition of a defendant’s DNA on an item or surface. According to the recommendations of the International Society of Forensic Genetics (ISFG) [1,2], evaluation of the DNA findings should be reported using a likelihood ratio (LR) approach based on case specific propositions. Activity level is addressed by Bayesian networks, a graphical tool to evaluate complex probabilities [2,3,4]. As the probabilities involve DNA transfer, persistence and recovery, an individuals’ shedder status may have an impact on the outcome. Fonneløp et al [5], found that the shedder status of an individual influenced the transfer rate of DNA to a

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