DNA deposited in whole thumbprints: A reproducibility study

Abstract

Touch DNA is pivotal in forensic science therefore understanding the mechanisms and variations of deposition and composition of genetic material in touched deposits is essential. Shedder status is still poorly understood, and the consistency and cohesiveness of research is less developed compared to other transfer and persistence considerations. In this study, the inter- and intra-variations between shedder categories and individuals were investigated by use of a nucleic acid binding dye. Ten volunteers deposited 30 thumbprints under two different time points post handwashing: 15 after a period of 15 min post handwashing (defined) and 15 after a period of at least 60 min post handwashing (undefined). Thumbprints were made on glass slides, marked with a grid of 55 squares, then the marks were stained with Diamond Dye and the cells that fluoresced in each square (7500 total) counted to determine the total number of cells. Shedders were less consistent in cellular deposition when thumbprints were made in the defined condition compared to waiting at least 60 min. Heavy shedders consistently generated informative profiles (defined here as 12 or more alleles); this occurred 73% of the time in the defined condition and 87% in the undefined. Intermediate shedders produced informative profiles, which occurred 50% of the time in the defined and 80% in the undefined condition. Light shedders consistently produced uninformative profiles with only 33% being considered uploadable to a DNA database for the defined condition and 27% informative for the undefined condition.