Australian Journal of Forensic Sciences Vol. 39, No. 2, December 2007, 107–122 RESEARCH PAPER STR genotyping of exogenous hair shaft DNA Kate S. Robertson a *, Dennis McNevin b and James Robertson a a Forensic and Technical, Australian Federal Police b Forensic Studies, School of Health Sciences, University of Canberra, Australia Most hairs found at crime scenes yield low quality and/or low quantities of nuclear DNA. This DNA is further depleted when stringent hair cleaning procedures are applied in the laboratory, suggesting that detectable DNA exists exogenously. The phenomenon of exogenous hair DNA is the subject of this study. DNA was extracted from washed and unwashed hairs and the resulting Profiler TM Plus STR genotypes were compared with those of reference (buccal) swabs from the hair donors. The DNA extraction procedure involved no prior cleaning of the hair sample and no dissolution of the hair during digestion, in contrast to standard procedures. The STR genotyping success was measured by recording the two dominant alleles at each locus and comparing them with the reference DNA profile. The effect of hair cleanliness was examined by leaving donors’ hair unwashed for periods of 1, 3 and 7 days before sampling. It was found that the genotyping success for unwashed hair was significantly higher than that for freshly washed hair, with the majority of clean hair samples producing little or no DNA. Genotyping success was also lower for donors with cosmetically treated hair compared with those having untreated hair. Although the quality of STR profiles (i.e. allele dropout, differential amplification) from hair shafts or telogen hair clubs is reduced compared with those from other biological sources, the genotypes obtained in this study may be usable and are certainly discriminating if alternative interpretational methods are applied. Keywords: Hair; shaft; telogen; extraction; short tandem repeat (STR); low copy number (LCN) 1. Introduction Hair is a biological tissue that can be very useful as forensic trace evidence in criminal investigations 9,8,34 . It can be used as evidence to exclude or associate individuals with a crime scene or object. Until recently microscopic examination of hair morphological characteristics has been the principal method of hair analysis 34 . A major limitation of hair microscopy includes its highly subjective nature, which makes it difficult for the hair examiner to place a statistical value on a proposed hair ‘match’. These issues have led to a greater focus on DNA analysis, which can potentially individualise DNA evidence with a very high statistical certainty. With the advent of the polymerase chain reaction (PCR) 29 , highly sensitive nuclear DNA (nuDNA) genotyping systems exist today, allowing identification of short tandem repeat (STR) microsatellite alleles from minute amounts of biological material 40,42 . *Corresponding author. Email: kate.robertson@afp.gov.au ISSN 0045-0618 print/ISSN 1834-562X online ß 2007 Australian Academy of Forensic Sciences DOI: 10.1080/00450610701650096 http://www.informaworld.com