TrueAllele® Casework validation on PowerPlex® 21 mixture data

J. Hornyak, W.P. Allan and M.W. Perlin, "TrueAllele® Casework validation on PowerPlex® 21 mixture data", Twenty Second International Symposium on the Forensic Sciences of the Australia and New Zealand Forensic Science Society, Adelaide, Australia, 2-Sep-2014.

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Abstract

DNA mixtures are a common form of biological evidence found at crime scenes. Newer STR multiplexes deployed in DNA laboratories can analyze twenty or more genetic loci, providing greater discriminating power when comparing mixture evidence to reference samples. Computer interpretation using Bayesian modeling considers many variables, eliciting considerable identification information from mixture data.

This study examined Cybergenetics TrueAllele® Casework, a computer modeling system. TrueAllele's sensitivity, specificity, and reproducibility were assessed on laboratory synthesized mixtures of known composition, amplified using Promega's PowerPlex® 21 STR panel. The reliability of TrueAllele probabilistic genotyping was tested on mixtures containing two, three or four contributors.

TrueAllele showed high sensitivity across each mixture group, giving only a few false exclusions with more contributors. The average match statistics were around sextillion with two contributors, hundred trillion with three contributors, and million with four contributors. The computer was specific, having a false positive rate of 0.0651% across the entire data set. The TrueAllele method was also highly reproducible, showing a within-group standard deviation of less than 1 ban for each contributor group. Sensitivity, specificity, and reproducibility were higher with fewer mixture contributors.

The study establishes that TrueAllele is a reliable DNA mixture interpretation method on PowerPlex 21 data.