Histological correlates of post mortem mitochondrial DNA damage in degraded hair M.T.P. Gilbert a, * , R.C. Janaway b , D.J. Tobin c , A. Cooper a , A.S. Wilson b,c a Henry Wellcome Ancient Biomolecules Centre, Department of Zoology, University of Oxford, South Parks Rd, Oxford OX1 3PS, UK b Department of Archaeological Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK c Department of Biomedical Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK Received 24 September 2004; received in revised form 16 February 2005; accepted 17 February 2005 Available online 11 April 2005 Abstract We have assessed the histological preservation of naturally degraded human hair shafts, and then assayed each for levels of amplifiable mitochondrial DNA and damage-associated DNA miscoding lesions. The results indicate that as sample histology is altered (i.e. as hairs degrade) levels of amplifiable mitochondrial DNA decrease, but no correlation is seen between histology and absolute levels of mitochondrial DNA miscoding lesions. Nevertheless, amplifiable mitochondrial DNA could be recovered across the complete range of the histological preservation spectrum. However, when template copy number is taken into consideration, a correlation of miscoding lesions with histology is again apparent. These relationships indicate that a potential route for the generation of misleading mitochondrial sequence data exists in samples of poor histology. Therefore, we argue that in the absence of molecular cloning, the histological screening of hair may be necessary in order to confirm the reliability of mitochondrial DNA sequences amplified from hair, and thus represents a useful tool in forensic mitochondrial DNA analyses. # 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Damage; Hair; Histology; Mitochondrial DNA 1. Introduction Hair has been used as a mitochondrial DNA (mtDNA) source for a range of genetic analyses, including forensic casework [1], medical screening [2], population genetic investigations [3] and recently, ancient DNA extractions [4,5]. On average, an individual sheds 100 hairs each day, making hair important forensic trace evidence [6]. Equally, the potential for non-invasive sampling of hair ensures that (a) in the case of archaeological remains the process is less destructive than with the use of other tissues such as bone or teeth and (b) with modern individuals the removal of a hair is also easy. The strong disulfide-bonded molecular structure of hair is derived from the high proportion of the protein keratin, which makes up the bulk of the fibre. Only a few specialised microorganisms are capable of utilising hair keratin as a sole nutrient source [7]. Thus, although in vivo yields of mtDNA per unit mass are not as great as bone or teeth, hair presents a useful source of mtDNA in forensic and ancient DNA analyses. Despite these advantages, as with other biological tis- sues, the DNA in hair can be expected to rapidly decay following death. It is believed that the majority of post mortem DNA damage directly hinders PCR amplification, through events such as inter-strand cross-linking and frag- mentation [8]. However, a small proportion of the damage does not hinder amplification, but results in the generation of www.elsevier.com/locate/forsciint Forensic Science International 156 (2006) 201–207 * Corresponding author. Present address: Ecology and Evolution- ary Biology, University of Arizona, 1041 E Lowell St., Tucson, AZ 85721, USA. Tel.: +1 520 621 4881/626 3456; fax: +1 520 621 9190. E-mail address: mtpgilbert@spymac.com (M.T.P. Gilbert). 0379-0738/$ – see front matter # 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.forsciint.2005.02.019