The forensic value of X-linked markers in mixed-male DNA analysis
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.
KeywordsMale mixtures Likelihood ratios Separation accuracy Similar amounts of DNA X-linked markers Forensic genetics
- 22.Lancia M, Severini S, Coletti A, Margiotta G, Dobosz M, Carnevali E (2011) Using x-chromosomal markers in rape investigation. Forensic Sci Int: Genet Suppl Ser 3(1):e55–e56Google Scholar
- 25.Gill P, Brenner CH, Buckleton JS, Carracedo A, Krawczak M, Mayr WR, Morling N, Prinz M, Schneider PM, Weir BS (2006) DNA commission of the International Society of Forensic Genetics. NA commission of the international society of forensic genetics: recommendations on the interpretation of mixtures. Forensic Sci Int 160:90–101CrossRefPubMedGoogle Scholar
- 29.Gill P, Gusmão L, Haned H, Mayr WR, Morling N, Parson W, Prieto L, Prinz M, Schneider H, Schneider PM, Weir BS (2012) DNA commission of the international society of forensic genetics: recommendations on the evaluation of STR typing results that may include drop-out and/or drop-in using probabilistic methods. Forensic Sci Int Genet 6:679–688CrossRefPubMedPubMedCentralGoogle Scholar