Participants: John M. Butler, Amy E. Decker, Peter M. Vallone, Margaret C. Kline, and Richard Schoske
Project Timeframe: July 2001 to July 2005
Purpose: Y-chromosome short tandem repeat (Y-STR) markers are being used as potential tools for distinguishing low levels of male DNA in the presence of excess female DNA as is present in many sexual assault samples. Usually single copy Y-STR loci produce a single amplicon in single source samples, and thus the observation of multiple peaks at such a locus could suggest to an analyst that a mixture of more than one male contributor is present in the tested sample. However, many regions of the Y-chromosome are duplicated or even triplicated in some individuals and this fact can thus complicate potential mixture interpretation.
Progress: Reasons for the presence of duplications at multiple loci within a single sample were explored in the context of Y-STR marker location along the chromosome. True male-male mixtures commonly exhibit more than one locus-specific PCR product across multiple Y-STR loci that are not adjacent to one another on the Y-chromosome. In addition, we found that duplicated loci typically possess alleles that differ by only a single repeat unit and possess similar peak heights.
Publications or Presentations Resulting From This Project:
Butler, J.M., Decker, A.E., Kline, M.C., Vallone, P.M. (2005) Chromosomal duplications along the Y-chromosome and their potential impact on Y-STR interpretation. J. Forensic Sci. 50(4): 853-859.
Butler, J.M. and Schoske, R. (2004) Duplication of DYS19 flanking regions in other parts of the Y chromosome. Int. J. Legal Med., 118: 178-183.
Butler, J.M. and Schoske, R. (2004) Forensic value of the multi-copy Y-STR marker DYS464. Progress in Forensic Genetics 10, Elsevier Science: Amsterdam, The Netherlands, International Congress Series 1261, 278-280.
John Butler workshop with Mike Coble to Northeastern Association of Forensic Scientists (NEAFS) (Rye Brook, NY), November 1, 2006, "Y-Chromosome and Mitochondrial DNA Analysis" [link to workshop webpage]
John Butler seminar at California Department of Justice DNA Laboratory (Richmond, CA), March 7, 2007, "Y-STRs: Markers, Mutations, and More" [.pdf]
Last updated: 06/19/2007
Disclaimer: This project was supported by National Institute of Justice Grant Number 2003-IJ-R-029, which is an interagency agreement between NIJ and the NIST Office of Law Enforcement Standards, awarded by the National Institute of Justice, Office of Justice Programs, US Department of Justice. Points of view in this document are those of the authors and do not necessarily represent the official position or policies of the US Department of Justice. Certain commercial equipment, instruments and materials are identified in order to specify experimental procedures as completely as possible. In no case does such identification imply a recommendation or endorsement by the National Institute of Standards and Technology nor does it imply that any of the materials, instruments or equipment identified are necessarily the best available for the purpose.