NCJ Number
212642
Journal
Journal of Forensic Sciences Volume: 50 Issue: 6 Dated: November 2005 Pages: 1361-1366
Date Published
November 2005
Length
6 pages
Annotation
Using a FBI genotypes dataset that contained complete genotype information from the 13 CODIS (Combined DNA Index System) loci for 959 individuals, this study computed all possible mixtures of 3 individuals in a DNA sample.
Abstract
The study examined allele sharing between pairs of individuals in the original dataset, a randomized dataset, and datsets of generated cousins and siblings, along with the number of loci that were necessary to determine the number of contributors present in simulated mixtures of four or less contributors. The relatively small number of alleles detected at most CODIS loci and the fact that some alleles are likely to be shared between individuals within a population can make the maximum number of different alleles observed at any tested loci an unreliable indicator of the maximum number of contributors to a mixed DNA sample. This research did not use other data available from the electropherograms (such as peak height or peak area) to estimate the number of contributors to each mixture. Thus, this study is a worst-case analysis of mixture characterization. Within this dataset, approximately 3 percent of three-person mixtures would be mischaracterized as two-person mixtures, and more than 70 percent of four-person mixtures would be mischaracterized as two-person or three-person mixtures, using only the maximum number of alleles observed at any tested locus. The authors favor the practice of many testing laboratories in reporting that a sample arises from "two or more individuals" when more than two alleles are observed at one or more loci during testing. 5 tables, 4 figures, and 13 references