Abstract
Due to improved laboratory techniques, touched surfaces and items are increasingly employed as sources of forensic DNA evidence. This has urged a need to better understand the mechanisms of DNA transfer between individuals. Shedder status (i.e. the propensity to leave DNA behind) has been identified as one major factor regulating DNA transfer. It is known that some individuals tend to shed more DNA than others, but the mechanisms behind shedder status are largely unknown. By comparing the amounts of DNA deposited from active hands (i.e. used “as usual”) and inactive hands (i.e. not allowed to touch anything), we show that some of the self-DNA deposited from hands is likely to have accumulated on hands from other parts of the body or previously handled items (active hands: 2.1 ± 2.7 ng, inactive hands: 0.83 ± 1.1 ng, paired t-test: p = 0.014, n = 27 pairs of hands). Further investigation showed that individual levels of deposited DNA are highly associated with the level of DNA accumulation on the skin of the face (Pearson’s correlation: r = 0.90, p < 0.00001 and Spearman’s ranked correlation: rs = 0.56, p = 0.0016, n = 29). We hypothesized that individual differences in sebum secretion levels could influence the amount of DNA accumulation in facial areas, but no such correlation was seen (Pearson’s correlation: r = − 0.13, p = 0.66, n = 14). Neither was there any correlation between DNA levels on hands or forehead and the time since hand or face wash. We propose that the amount of self-DNA deposited from hands is highly influenced by the individual levels of accumulated facial DNA, and that cells/DNA is often transferred to hands by touching or rubbing one’s face.
Highlights
Handled items and surfaces are commonly encountered at crime scenes and are often used as sources of DNA evidence
DNA deposition from active versus inactive hands First, we investigated whether deposited DNA from hands were more likely to originate from shed cells/DNA from the hands themselves, or from extrinsic sources, i.e. from touching other body parts or previously handled objects that carry residual cells/DNA
A higher level of DNA was retrieved from the active hand in 23 of the 27 pairs of hands, but the differences between active and inactive hands varied considerably
Summary
Handled items and surfaces are commonly encountered at crime scenes and are often used as sources of DNA evidence. E. individuals that consistently deposit more or less DNA [3,11,12,13], there is evidence that the quantity of deposited DNA varies from time to time for most persons [10,14]. This suggests that some factors appear to steadily influence the shedder status of a person over time, conditional factors such as behaviour, environment and activity have an impact in a given situation. The underlying mechanisms controlling DNA shedding, and the impact of genetic versus various non-genetic conditional factors, are not yet clear
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