Discovering the Optimal Hair Sections for Mitochondrial DNA Quantification via a Multiplex Real-Time PCR Assay

Abstract

Hair is among the frequently encountered evidence found in crime scenes. The average person loses approximately 100 hairs a day. Because these hairs are telogen strands, or at the end of their life-phase, there is very little tissue present to obtain nuclear DNA. Hair shafts, however, contain mitochondrial DNA that can be used for identification purposes. There are two areas of concern involving mtDNA analysis of hair shafts: 1) will there be enough mtDNA present to obtain a full profile, and 2) and has the integrity of mtDNA been compromised due to oxidative properties, and/or the keratinization of the hair. The purpose of this project is to elucidate whether the amount of mitochondrial DNA changes from the proximal to the distal end of the hair shaft. Five hair samples were obtained from five subjects and the hairs were dissected at every fourth centimeter. DNA was extracted from each hair section, and subjected to mitochondrial DNA quantification (via the control region of the genome), as well as assessed for any deletions seen within the coding region as a sign of damage that may have occurred, using an assay validated by the University of North Texas- Health Science Center (UNTHSC, Fort Worth, Texas). It was found that there was generally a gradual decrease in mitochondria copy number throughout the hair strands from the proximal to the distal end. Also, it was found that mitochondrial DNA is more susceptible to damage towards the distal end. Mitochondrial DNA sequencing was performed on specific samples to observe any relationship between the concentration of mitochondria and the stability of the sequence.