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Forensic Biology Unit Implements State-of-the-Art Software Tool for DNA Mixture Analysis

Wednesday, May 2, 2018

The Forensic Biology Unit was one of the first laboratories in the US to implement a state-of-the-art software tool for DNA mixture analysis known as STRmixtm. The Unit’s work is now part of a published collaborative study, along with 30 other US and international laboratories, to satisfy concerns of DNA mixture analysis raised by the President’s Council of Advisors on Science and Technology (PCAST). The results demonstrate that laboratories using the STRmixTM software are able to analyze DNA results far more complex than the limitations proposed by PCAST.


We report a large compilation of the internal validations of the probabilistic genotyping software STRmix™. Thirty one laboratories contributed data resulting in 2825 mixtures comprising three to six donors and a wide range of multiplex, equipment, mixture proportions and templates. Previously reported trends in the LR were confirmed including less discriminatory LRs occurring both for donors and non-donors at low template (for the donor in question) and at high contributor number. We were unable to isolate an effect of allelic sharing. Any apparent effect appears to be largely confounded with increased contributor number.