Separating familial mixtures, one genotype at a time

R. David, M. Bowkley and M.W. Perlin, "Separating familial mixtures, one genotype at a time", Northeastern Association of Forensic Scientists 40th Annual Meeting, Hershey, PA, 4-Nov-2014.

Talk

PowerPoint presentation with live audio recording of Mr. Bowkley's talk.

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Abstract

TrueAllele Casework^® can separate out genotypes from complex mixtures that contain multiple family members. Genotype separation overcomes high allele sharing and produces simple likelihood ratios (LR).

One recent father-daughter rape case had multiple cuttings from a blanket, with evidence items that were two person mixtures. TrueAllele first assumed that two unknown people contributed their DNA to the evidence, and inferred genotypes matching the father and daughter with statistics in the tens of trillions. Next, assuming the father as a known contributor to the evidence, the added information better separated the genotypes, more strongly matching the daughter at the hundred quadrillion level. A sister reference was excluded via a negative log(LR) value.

TrueAllele's "peeling" method separates genotypes layer-by-layer from a complex mixture. Cybergenetics has used peeling in several cases containing extremely complex mixtures of family members having up to five related contributors. Peeling away major contributors before minor ones lets TrueAllele separate out the genotypes, even when family relationships exhibit many shared alleles.

This talk illustrates the peeling method through casework examples, and shows how it can increase genetic identification information.