A jacket is found discarded near a crime scene. The blood stains test positive for the victim’s DNA. Other areas of the jacket also contain DNA from an unknown subject. Was the jacket worn or just touched by this other person? This is often a courtroom debate.
Magee, et al from Forensic Science Ireland performed a study on DNA transfer from wearers and non-wearers to the collars and cuffs of worn clothing.1 The wearer was always detected as the major profile from both collars and cuffs, when a profile could be obtained, though there was quite a bit of variability in the amount of DNA recovered. They found that more wearer DNA is found on collars than cuffs; and there was more non-wearer DNA found on cuffs than collars. There did not seem to be a correlation between amount of time worn and the quantity of DNA recovered – meaning other factors, such as shedder status or how the skin and fabric were in contact, were contributing to the process.
Magee and Fonneløp, et al discussed ways that non-wearer DNA might come to be on clothing. The first would be from family members living in the same household while sources could be from office mates and even just environmental background DNA.2
The lab mini-taped collars and cuffs of jackets, sweaters, hoodies, shirts, blouses and T-shirts that were made from cotton, polyester, wool and a variety of other fabrics. DNA was extracted and then quantified using the Applied Biosystems Quantifiler Duo kit. STR analysis was performed with the Applied Biosystems NGM Select kit and the 3500 Genetic Analyzer. The analysis is based on quantity of DNA recovered as well as mixture status (major and minor contributors found) and the paper provides guidance on how they interpreted the results.1
The paper concluded that DNA is more likely to be obtained from collars than cuffs, the major profile obtained is more likely to be the wearer than the non-wearer, though on the rare occasion the non-wearer may contribute more DNA (from a cuff in this instance), and that wearing a garment for at least 2 hours produces more DNA than a brief touch. The paper wraps up with an example of all the statistics used to evaluate DNA quantities in scenarios of wearing or touching which may prove useful to many labs as they work though case evidence. 1
It’s also well known that DNA is more difficult to extract from some fabrics than others. And these items of clothing may also have been exposed to challenging environmental conditions or be covered in blood or other inhibitors that are co-extracted. Learn more if you are faced with analyzing these challenging forensic DNA samples types.
1. Alan M.Magee, Michelle Breathnach, Stephen Doak, Fiona Thornton, Conor Noone, Louise G.McKenna, Wearer and non-wearer DNA on the collars and cuffs of upper garments of worn clothing, Forensic Science International: Genetics https://doi.org/10.1016/j.fsigen.2018.02.011
2. Fonneløp, Ane Elida et al. The implications of shedder status and background DNA on direct and secondary transfer in an attack scenario. Forensic Science International. https://doi.org/10.1016/j.fsigen.2017.03.019
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