The forensic value of X-linked markers in mixed-male DNA analysis

Abstract

Autosomal genetic markers and Y chromosome markers have been widely applied in analysis of mixed stains at crime scenes by forensic scientists. However, true genotype combinations are often difficult to distinguish using autosomal markers when similar amounts of DNA are contributed by multiple donors. In addition, specific individuals cannot be determined by Y chromosomal markers because male relatives share the same Y chromosome. X-linked markers, possessing characteristics somewhere intermediate between autosomes and the Y chromosome, are less universally applied in criminal casework. In this paper, X markers are proposed to apply to male mixtures because their true genes can be more easily and accurately recognized than the decision of the genotypes of AS markers. In this study, an actual two-man mixed stain from a forensic case file and simulated male-mixed DNA were examined simultaneously with the X markers and autosomal markers. Finally, the actual mixture was separated successfully by the X markers, although it was unresolved by AS-STRs, and the separation ratio of the simulated mixture was much higher using Chr X tools than with AS methods. We believe X-linked markers provide significant advantages in individual discrimination of male mixtures that should be further applied to forensic work.

Application of X-STRs for Forensic Identification in Mixed DNA Profile: A Case Report

“…Thanks to these results and biological reasoning, in the absence of further scientific work concerning the application of X-STRs in forensic cases of biological mixtures created by contributors also of different sex, this work aims to encourage the scientific forensic community to the use of X-STRs for discriminatory purposes. Their application could, in fact, be decisive for a correct deconvolution of the mixtures and consequent identification of the contributing contributors, even if of different sex [15].…”

“…It is also applied in cases of missing persons, incest and finally in the identification of victims of attacks and mass disasters (DVI) [14]. However their use in criminal cases, and in particular in the study of mixed traces, is still rather rare [15].…”

“…Few studies have been made on forensic cases [13,15], in which however the use of X Chromosome markers has been decisive, such as for example mixtures from vaginal swabs of women victims of rape, in which suspects were related between them, and analysis of both autosomal and Y chromosome STRs were not conclusive [13].…”

Application of X-STRs for Forensic Identification in Mixed DNA Profile: A Case Report

“…Currently, there are a lot of publications regarding the development and validation of new X-STR markers for forensic purposes [18][19][20][21][22], especially for kinship determination and complex kinship discrimination [23,24]. However, their use in criminal cases, especially in the study of mixed traces, is still rather rare [25].…”

“…Few studies have been conducted on criminal cases [13,25], in which, however, the use of X-STRs has been decisive. For example, in cases of mixtures taken from vaginal swabs of female victims of rape, the suspects were related and the analyses of both autosomal and Y-Chromosome STRs were not conclusive [13].…”