Professor Adrian Linacre, Chair in Forensic Science at Flinders University, South Australia joined us at HIDS Rome to discuss his lab’s latest findings on the analysis of touch DNA from crime scene evidence samples.
Touch DNA analysis can be a vital part of casework. It may be that just a few cells will be deposited on a critical piece of evidence. Think about touching the screen of a cell phone, or closing a zip lock baggie. These are just the types of samples that the Linacre lab has analyzed.1
There are two recommendations that he makes to labs that are looking to optimize their protocols. First, a DNA binding dye may be used to visualize the cells on the evidence AND then see those cells transfer to the swab.2 Next, a lab might also use direct PCR, without a DNA extraction step, right off the swab; DNA extraction may result in the loss of 20-80% of an already minute amount of DNA.
Dr Linacre’s lab has used both GlobalFiler and Identifiler Plus kits to generate DNA profiles. They use the same validated processes and protocols for cycling, which means these methods could easily move into casework labs’ SOPs.
There may be regulatory guidelines that prohibit a lab from using the direct PCR method. Such guidelines include the requirement of a DNA quantification step, and avoiding the consumption of the entire sample that would leave no sample available for retesting. It’s certainly worth revisiting the discussion on direct PCR to see what the community needs to move forward with implementation strategies.3
You can also download Dr Linacre’s HIDS presentation as he relates more on these more sensitive methods for analyzing trace evidence.
- Belinda Martin, Renee Blackie, Duncan Taylor, Adrian Linacre, DNA Profiles Generated from a Range of Touched Sample Types, Forensic Science International: Genetics https://doi.org/10.1016/j.fsigen.2018.06.002
- Shedding light on shedders. Kanokwongnuwut, Piyamas et al. Forensic Science International: Genetics , Volume 36 , 20 – 25.https://doi.org/10.1016/j.fsigen.2018.06.004
- Direct PCR amplification of forensic touch and other challenging DNA samples: A review. Cavanaugh, Sarah E. et al. Forensic Science International: Genetics , Volume 32 , 40 – 49. https://doi.org/10.1016/j.fsigen.2017.10.005
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