This report examines the impact of duplicated and even triplicated regions of the Y-chromosome and how this influences an assessment as to whether or not a mixture of multiple male DNA is present in an evidentiary sample, which could be the case in a gang rape.
A total of 650 anonymous liquid blood samples with self-identified ethnicities were purchased and determined to be unique and single-source. The PowerPlex Y kit was used to amplify the Y-STR loci. The separation and detection of Y-STR PCR products were done with either the ABI Prism 310 or the ABI Prism 3100 Genetic analyzer 16-capillary array system. Following data collection, samples were analyzed with Genescan 3.7, and allele designations were made in Genotype 3.7. Several samples showed duplications at multiple Y-STR loci. This report explains how the Y-STR marker duplication might initially occur and then independently mutate over generations. In order to determine whether the Y-STR locus duplication could be differentiated from a true male-male mixture, a sample that contained two different males was tested with the PowerPlex Y kit. Based on this analysis, guidelines are provided for deciphering whether a sample is a mixture of more than one male or is a single male with a locus duplication. 4 figures, 2 tables, and 29 references