DNA Levels from Everyday Activities

Abstract

This project aimed to investigate the detection of background levels of DNA, in particular using the PowerPlex®Y Y STR DNA testing method, supplemented with Identifiler® autosomal STR DNA testing. Sexual assaults are a common crime in New Zealand, which when reported to the police can result in a full body medical examination being carried out on a complainant or person of interest by DSAC personnel using a medical examination kit (MEK). No research has been previously carried out with un-used MEKs or items within an un-used MEK to confirm that they are DNA-free prior to use. Therefore the first part of this project involved both Y STR and autosomal DNA testing on various items from a single un-used MEK. Y STR and autosomal analysis indicated that no DNA was detectable in all items tested. These findings therefore confirm that the MEKs are fit for purpose and that any male or human DNA detected in samples collected using items from an MEK are more likely to be inherent to the samples than to the manufacturing and packaging of the MEK itself. The main body of the project was divided into three sections that used 8 participants to focus on determining if background levels of male DNA could be detected from a range of various everyday scenarios. The first section looked at background DNA on a new garment that was stored and laundered in participant’s homes. Results indicated that both storing and laundering can result in the transfer and persistence of DNA onto a garment, with most of the DNA detected being able to be explained by comparison to household member’s reference profiles. Also noted was the washing machine may act as a vector for DNA transfer. The second looked at the level of background DNA on skin before and after a routine day’s activities by sampling the upper chest area and the lower front waist. Y STR DNA profiling results indicated that in about 50% of samples male DNA could be detected, suggesting transfer and persistence of DNA on skin as a result of everyday activities is likely, with activities including a day at the office right through to social scenarios. Autosomal DNA testing of these samples indicated that large amounts of donor DNA are likely to be found on skin. The third part looked at background male DNA that can be found on a communal seating area of the home such as a couch as well as the amount of this DNA that can transfer onto clothing after contact due to someone sitting here. Results indicated that very little if any male DNA can transfer onto and persist on fabric that has contacted a communal seating area of the home by passively sitting on the couch. These findings suggest that adventitious transfer onto clothing as a result of a normal activity such as sitting may be able to be disputed. With the testing carried out in relation to background levels of DNA on garments, skin and within the home, it was found that it was unlikely that any DNA detected would be foreign to the donor or people they reside with. The results from this and other similar studies may be useful in determining the likelihood of alternative scenarios presenting the same DNA results.