Prevalence of DNA from the driver, passengers and others within a car of an exclusive driver.

Cars are often sampled for DNA to help identify occupants and their possible location(s) within the car. While DNA from the frequent driver is likely to accumulate over time, DNA from previous and/or subsequent occupants, and those whose DNA has inadvertently been transferred to the car, may also contribute to any samples collected. This study investigates how much DNA resides on various sites within cars, and who might contribute to these samples. A total of 35-36 sites, internal and external, were targeted within four cars with sole long-term drivers. In addition to the car keys, sample sites included the exterior and interior door handles (driver and passenger sides), through to the internal compartments (driver side, middle area and front passengers' side). Reference samples were collected from the exclusive drivers, their co-resident partners and, where possible, recent passengers. The driver was always observed as a contributor in DNA profiles from the driver's side and, in most instances, was the sole, major or majority contributor to the profile. The driver was also observed as a major, majority or minor contributor at several sites on the passenger side. DNA of known recent passengers, close associates of the driver and unknown individuals was collected from many sites on both the driver and passenger sides. These findings may assist in sample targeting within cars and in the evaluation of DNA evidence when propositions relate to the activities performed.

Shedder status-An analysis of self and non-self DNA in multiple handprints deposited by the same individuals over time.

There are several studies that suggest that different people deposit different quantities of their own DNA on items they touch, i.e. some are good shedders and others are bad shedders. It is of interest to determine if individuals deposit consistent quantities of their own DNA, no matter the occasion, as well as the degree of variability among individuals. To investigate this, participants were tested for their ability to deposit DNA by placing right and left handprints on separate DNA-free glass plates at three set times during the day (morning, midday and afternoon) on four different days spaced over several weeks. Information regarding recent activities performed by the individual was recorded, along with information on gender, hand dominance and hand size. A total of 240 handprint deposits were collected from 10 individuals and analyzed for differences in DNA quantity and the type of the DNA profile obtained at different times of the day, on different days, between the two hands of the same individual, and between different individuals. Furthermore, the correlation between the deposit quantity and the ratio of self to non-self DNA in the mixed deposits was analyzed to determine if the amount of non-self DNA has an effect on overall DNA quantities obtained. In general, this study has shown that while there is substantial variation in the quantities deposited by individuals on different occasions, some clear trends were evident with some individuals consistently depositing significantly more or less DNA than others. Non-self DNA was usually deposited along with self DNA and, in most instances, was the minor component. Incidents where the non-self portion was the major component were very rare and, when observed, were associated with a poor depositor/shedder. Forensic DNA scientists need to consider the range and variability of DNA a person deposits when touching an object, the likelihood of non-self DNA being co-deposited onto the handled object of interest and the factors that may affect the relative quantity of this component within the deposit.