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The Science of Quantitative DNA Mixture Interpretation
M.W. Perlin, "The science of quantitative DNA mixture interpretation", Scientific Working Group on DNA Analysis Methods (SWGDAM), Fredericksburg, VA, 11-Jan-2011
PowerPoint presentation with live audio recording of the Scientific Working Group on DNA Analysis Methods 2011 talk.
Questions and Answers
SWGDAM asked Cybergenetics five questions about the TrueAllele® Casework system. Here are concise answers that are expanded upon in the thirty minute presentation.
- What advancements have been made in your casework software that would make the software eligible to be a casework expert system?
TrueAllele completely models quantitative STR data, including peak uncertainty. Without those features, DNA interpretation would only be guesswork and often incorrect. The TrueAllele VUIer software enables rapid and visual preparation of flexible match statistic reports, including co-ancestry and confidence intervals.
- Are there issues that are still being addressed prior to releasing to laboratories for this consideration?
There are no issues. TrueAllele has been released to laboratories for forensic use. Cybergenetics works closely with TrueAllele groups to ensure a smooth deployment. Cybergenetics provides process planning, education, training, documentation, data assessment, validation services, ongoing meetings, project management, workflow integration and testifying support.
- Why can it be relied upon as a casework expert system?
TrueAllele has multiple published validation studies, and has been admitted into evidence in US courts. Reporting is done using the well-accepted likelihood ratio framework. Cybergenetics has experience testifying about TrueAllele results in admissibility hearings and at trial.
- Specifically, how are mixtures addressed?
TrueAllele explores all possible genotype and mixture weight combinations (along with other important variables). This computer search determines how well each genotype explains the quantitative data, thereby assigning probability values to allele pairs. A likelihood ratio is then calculated from these genotype probabilities.
- How are peak height differences addressed in terms of degradation vs. mixture?
TrueAllele can determine the extent of each contributor's DNA degradation using additional model variables. So the effective amount of DNA for each contributor (based on fragment size) is accounted for when computing mixture weight at a locus. Modeling both degradation and mixture weight can better explain peak height data, and thus more accurately infer genotypes.