Parameters affecting the recovery of human chromosomal DNA from touched evidence suitable for subsequent DNA typing was investigated. A model system was devised in which approximately equal numbers of male and female volunteers created a touch impression on clean glass slides with either the thumb or forefinger. Material deposited on the slide was then lifted using a Dacron swab wetted with dilute buffer solution and then subjected to extraction and quantitation of the DNA recovered. Chromosomal DNA present on each slide was quantitated using a sensitive, human-specific assay. Individuals providing touched slides for the study were categorized as heavy, intermediate, and light shedders, depending upon the amount of DNA recovered from their glass slides. Results showed that male donors were more often classified as heavy shedders (26%) when compared with female donors (12.5%), who tended to be classified as intermediate shedders (66.7%). In both sexes, only about 20% of donors were classified as light shedders. When items touched with the forefinger or thumb from the dominant versus nondominant hand from both sexes were compared, the nondominant hand deposited significantly more DNA on glass slides than did the dominant hand. Different types of mock forensic evidence, including knives, guns, and bullet casings, were found to serve as suitable substrates for the recovery of DNA when handled by heavy or intermediate shedders. Interestingly, DNA deposited on bullets handled during the loading of 22 and 9 mm caliber handguns survived firing of the weapons and could be recovered for STR analysis.
|Number of pages||9|
|Journal||Journal of Forensic Identification|
|Publication status||Published - 1 Jan 2008|