DNA transfer—a never ending story. A study on scenarios involving a second person as carrier

Abstract

The transfer of DNA directly from one item to another has been shown in many studies with elaborate discussions on the nature of the DNA donor as well as material and surface of the items or surrounding features. Every DNA transfer scenario one can imagine seems to be possible. This evokes more and more intricate scenarios proposed by lawyers or attorneys searching for an explanation of the DNA of a certain person on a distinct item with impact on a crime. At court, the forensic genetic scientist has to comment on the probability of these scenarios thus calling for extensive studies on such settings. Here, the possibility of an involvement of a second person as a carrier of the donor's DNA in a variety of different scenarios including three pairs of people and two kinds of items (textiles and plastic bags) was investigated. All transfer settings were executed with and without gloves on the carrier's hands. DNA left on the items was isolated and analyzed using the Powerplex® ESX17 kit. In 21 out of 180 samples, all alleles of the donor DNA could be obtained on the second item (12%), on eight samples, the donor's DNA was dominant compared to all other alleles (38% of samples with complete donor profile). Additionally, 51 samples displayed at least more than half of the donor's alleles (28%). The complete DNA profile of the carrier was found in 47 out of 180 samples (42 partial profiles). In summary, it could be shown that a transfer of donor DNA from epithelial cells through a carrier to a second item is possible, even if the carrier does not wear gloves.

DNA detection of a temporary and original user of an office space

“…Reasons for this could be due to these surfaces being the largest within the experiment, having been sampled using tape lifts in Lab B, and being the surfaces touched for the longest duration, as well as them being the only fabric surfaces sampled. Several studies have shown that in general, fabric substrates pick-up and retain DNA better than non-porous substrates [20][21][22][23]. Furthermore, the relatively higher number of contributors to profiles generated from the chair seats and backrests may indicate that clothing picks up DNA from locations it comes into contact with and transfers some of it to these items when the person wearing the clothing sits on the chair, where it can accumulate [18,24].…”

A review of trace “Touch DNA” deposits: Variability factors and an exploration of cellular composition

“…DNA has been demonstrably transferred by handling both with and without gloves [97], from a range of items to both secondary and tertiary objects [98]. The transferred DNA may yield profiles ranging in quality from non-existent to complete and database-uploadable [97,98], following either prolonged or brief social contact [99], leaving unpredictability (see Table 2).…”

“…Proof-of-concept studies report the deposition of DNA to greater or lesser degrees on surfaces that collect DNA well or not. DNA has been recovered successfully from a wide range of substrates including metal cables [6], lipstick [101], car interiors [102], shoes [42,103], firearms and ammunition [104,43], plastic bags [97,105], sheets [78], paper [106,107], and of course, fingerprints [30,108]. Generally rough and porous surface are reported to be superior collectors of DNA to smooth ones; wood is preferable to fabrics followed by glass [8], cotton being better than plastic upon consistent handling [48].…”

“…Historically, scientists assumed DNA deposited by touch came from sloughed off outermost skin cells [31], and that narrative persists in courtroom testimony and publications today [41,42,49,81,97], despite limited evidence to support it. Data in studies of touch deposits is typically in the form of DNA typing results rather than any microscopy or cellular characterization, thus demonstrating empirically only the presence of DNA and not its provenance.…”

Most Common Medico-Legal Autopsy-Related Human and Nonhuman Biological Samples for DNA Analysis

“…Despite increased attention, and due to the development of more and more sensitive DNA analysis, alternative scenarios are always represented, involving DNA transfer through a secondary person or medium. The minute amount of a few cells or DNA molecules, which may be applicable for amplification, is not recognizable typically in an autopsy environment and is easily transferable between cases [4,117,118]. Although methodological developments are continuously making efforts to eliminate the effect of contamination artifacts from the profiling process [119,120], less appropriate autopsy sampling, incorporating the undetected contamination incidents, can lead to false interpretation within a DNA laboratory [5].…”