DNA mixtures Tag

Can we rely on the DNA match statistic from specialist statistical software?

DNA match statistic terms forming an image of a diceAs DNA profiling methods have become ever more sensitive, the detection of trace amounts of DNA has significantly improved. As a result, the number of DNA mixtures we encounter has increased.  This was especially highlighted following the introduction of DNA17 methods in 2014. In many situations the mixtures have multiple contributors and are complex to interpret.  Whilst previously many results were designated as too complex for interpretation, the last few years have seen the introduction of ‘probabilistic genotyping software’ packages which enable a statistical evaluation of complex results.

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DNA transfer: A question of how and when

Cartoon of Mr Red and Mr Yellow shake hands and transfer their DNA to the other personIn recent years, forensic science has seen a number of significant improvements in the field of forensic DNA analysis.  One of the drivers has been the need to detect ever decreasing amounts of DNA.  The DNA17 technique, in routine use in the UK since July 2014, is much more sensitive than its predecessor SGMPlus, and therefore the spotlight is shining brightly on the issues around DNA transfer and persistence.

What does the presence of an individual’s DNA on an item related to a crime actually mean in the context of the case circumstances?  The presence of a DNA match to a suspect’s profile tells you nothing about how or when the DNA got there.  Scenarios incorporating multiple DNA transfer steps, rather than a single direct transfer, are increasingly being raised in court as potential means for the presence of the defendant’s DNA at the crime scene or on an evidential item.

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The end of Dlugosz style DNA evidence in court?

Graphic of DNA molecule with DNA profile overlay

Last week the Forensic Science Regulator released long-awaited guidance in the area of DNA mixture interpretation. Whilst this document is still a draft for consultation and therefore not the final version, the main UK forensic providers have all had input and therefore changes are likely to be minimal.

 

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Streamlined Forensic Reporting – the hidden truth

Dictionary entry for evidence - forensic evidence is now commonly reported using streamlined forensic reportsStreamlined Forensic Reporting (SFR) was rolled out nationally in April 2013.  The CPS guidance document states that  “SFR is a revised case management procedure for producing forensic evidence at court, which seeks to reduce unnecessary costs, and delay in the criminal justice system. The process takes a more proportionate approach to forensic evidence through the early preparation of a short report that details the key forensic evidence the prosecution intend to rely upon.  The aim is to achieve early agreement with the defence on forensic issues but where this cannot be achieved in the first instance, to identify the contested issues.”

The first stage SFR1 report is not a witness statement or report to which the Criminal Procedure Rules apply.  It is, at this stage, difficult for the defence to determine whether they dispute the evidence being provided as the information that the SFR1 provides is often nothing more than a bland description of the analytical result, with little if any background or interpretational information.  READ MORE

Demonstrating that penetration has occurred when no semen is found: the whys and wherefores of Y-STRs

Human chromosomes - Y-STR tests areas of the Y chromosome

Evidence to demonstrate that penile or digital penetration of the vagina has taken place can be difficult to find in some cases.  Traditional DNA profiling techniques can’t really help as the few male cells potentially deposited are overwhelmed by the large amount of female DNA present in the vaginal cells.  Y-STR typing is a form of DNA analysis that targets just the DNA present on the male Y chromosome allowing production of a male Y-STR profile even in the presence of seemingly overwhelming amounts of female DNA.READ MORE