Sex-specific age association with primary DNA transfer.

Practicing forensic scientists who are called to provide expert witness testimony are often asked to explain both the presence and the absence of DNA on objects that have been handled by perpetrators with bare hands. Unwashed hands, depending on what they have come in contact with previously, may become the vehicle of both primary and secondary transfer of DNA. In this study, we investigated the propensity of primary and secondary transfer of DNA from unwashed bare hands of 128 individuals onto plastic tubes. Our experiments, carried out in triplicate, have shown that DNA was not detected on all the touched tubes, secondary transfer of DNA, through unwashed hands, was small, and in the majority of cases primary DNA transfer could be distinguished from secondary DNA transfer. A statistically significant association was demonstrated between percent DNA profile deposited on plastic tubes, through unwashed hands, and the age of male individuals.