MITOCHONDRIAL DNA OF DOG'S HAIR

Mitochondrial DNA of Dog's Hair

Mitochondrial DNA of Dog's Hair

Introduction

Identifying fibres or hairs that share a common source can provide a valuable link between evidential items in forensic investigations. Whilst much has been published on the identification of textile fibres and their transfer, relatively little is available for animal hair. Because cats and dogs shed hairs more frequently than humans, their hairs readily undergo both primary and secondary transfer and consequently are found at a significant proportion of crime scenes. However, identification is seldom taken beyond the species level as so much variation in morphology and colour can occur within a single individual (Alvarez, 1996, pp.125-9).

Greater discrimination can be achieved through DNA analysis, as all hairs from a single individual possess the same DNA sequence except for rare cases of somatic variation. Highly variable nuclear short tandem repeat (STR) loci cannot be reliably typed from single dog hairs but this is seldom a problem when analysing mitochondrial DNA (mtDNA) due to its higher copy number. Two analyses are possible—species determination, which is achieved by comparing cytochrome b gene sequences and discrimination between individuals using control region sequences. Due to extensive sequence polymorphism within the 50 hypervariable region (50 HVR), many individuals can be excluded as potential sources and the likelihood of a chance match can be estimated from a database of mitochondrial DNA variants (Brevnov, 2009, pp.599-607).

Published studies have reported mitochondrial DNA sequence variation in dogs, and the use of short control region sequences from dog hairs in forensic casework. In this study, we aimed to develop a robust forensic method for amplifying and sequencing the majority of polymorphic control region sites from single hairs. To support the application of this method, a database of sequence variation among sampled UK dogs was created and compared with published data from other populations. The survey also allowed an estimate of the frequency of heteroplasmy and potential recurrent mutations that might have a significant bearing on the interpretation of single base differences between evidential samples.

Nuclear and mitochondrial DNA of human origin has proven their importance in criminal investigation for human identification purposes, as well as for establishing a link between crime scenes and certain persons. Currently, forensic DNA analysis is being extended to cover the usage of DNA from other species involved in crime. This extension includes the usage of DNA from microorganisms (viruses, bacteria, etc.) and macroorganisms (dogs) and covers both the species level and the individual level. Our study describes the first attempt in UK to use dog's DNA analysis (nuclear and mitochondrial DNA) in a criminal investigation (Corte, 2006, pp.710-712).

Discussion

Shed hairs are one of the most commonly found evidence materials at crime scenes. A human perpetrator can leave hairs originating not only from himself but also from animals in his possession, directly or indirectly from his clothes, making analysis of animal hairs an important tool for forensic casework. DNA analysis has been used as a forensic method for more than 15 years ...