title: Estimating the number of contributors to two-, three-, and four-person mixtures containing DNA in high template and low template amounts.
abstract: OBJECTIVE
  To develop guidelines to estimate the number of contributors to two-, three-, and four-person mixtures containing either high template DNA (HT-DNA) or low template DNA (LT-DNA) amounts.
  
  
  METHODS
  Seven hundred and twenty-eight purposeful two-, three-, and four-person mixtures composed of 85 individuals of various ethnicities with template amounts ranging from 10 to 500 pg were examined. The number of alleles labeled at each locus and the number of labeled different and repeating alleles at each locus as well over all loci for 2 HT-DNA or 3 LT-DNA replicates were determined. Guidelines based on these data were then evaluated with 117 mixtures generated from items handled by known individuals.
  
  
  RESULTS
  The number of different alleles over all loci and replicates was used to initially categorize mixtures. Ranges were established based on the averages plus and minus 2 standard deviations, and to encompass all observations, the maximum and the minimum values. To differentiate samples that could be classified in more than one grouping, the number of loci with 4 or more repeating or different alleles, which were specific to three- and four-person mixtures, were verified. Misclassified samples showed an extraordinary amount of allele sharing or stutter.
  
  
  CONCLUSIONS
  These guidelines proved to be useful tools to distinguish low template and high template two-, three-, and four-person mixtures. Due to the inherent higher probability of allele sharing, four-person mixtures were more challenging. Because of allelic drop-out, this was also the case for samples with very low amounts of template DNA or extreme mixture ratios.
authors.affiliation: Office of Chief Medical Examiner of the City of New York, The Department of Forensic Biology, New York, NY 10016, USA.
authors.forename: Jaheida
authors.initials: J
authors.lastname: Perez
authors.forename: Adele A
authors.initials: AA
authors.lastname: Mitchell
authors.forename: Nubia
authors.initials: N
authors.lastname: Ducasse
authors.forename: Jeannie
authors.initials: J
authors.lastname: Tamariz
authors.forename: Theresa
authors.initials: T
authors.lastname: Caragine
mesh_terms: D000483:Alleles; D004247:DNA / Q000032:analysis*; D005006:Ethnicity / Q000706:statistics & numerical data*; D005784:Gene Amplification / Q000235:genetics*; D006801:Humans; D018895:Microsatellite Repeats / Q000235:genetics*; D017410:Practice Guidelines as Topic; D014481:United States
chemical_list: D004247:DNA