Thursday, November 26, 2020

Obtaining DNA from fingermarks

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Michael Whyte
Crime Scene Officer and Fingerprint Expert with over 7 years experience in Crime Scene Investigation and Latent Print Analysis. The opinions or assertions contained on this site are the private views of the author and are not to be construed as those of any professional organisation or policing body.
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DNA fingerprinting was first developed in 1985 at the UK’s University of Leicester, but generally needs more than a fingerprint to work – it relies on skin cells, blood, hair or saliva. Researchers in Australia have developed a technique that could extract and multiply the DNA and create a direct DNA profile simply from fingermarks left behind at the scene of a crime.

DNA lifted from fingerprints is generally in very small quantities and may be degraded or contaminated, which limits its use as evidence. The team, from Flinders University, avoided the extraction step usually used in generating DNA profiles, which can result in loss of DNA, or in contamination from extraneous DNA, both of which would cause problems in very sensitive analysis of small samples. Instead, they collected the DNA from fingermarks using positively-charged fibres from a swab moistened with the non-ionic surfactant Triton-X, and added the fibres directly into the PCR tube. The volunteers made the fingermarks 15 minutes after hand washing.

After 29-30 cycles of PCR, depending on the technology used, the researchers analysed the DNA. Out of 170 fingermarks from 34 people, 71% (122 DNA profiles) included 12 or more alleles, and less than 2% (4 samples) yielded no DNA. No DNA was found in swabs taken immediately after hand washing.

However, 15 minutes after handwashing, there is an approximately 66% to 74% chance of gaining a DNA profile with 12 or more alleles, with many full DNA profiles being observed.

The South Australia Police Service requested a DNA profile from a fingermark on tape wrapped around a drug seizure. The team optimised the technique and created a DNA profile that showed 31 dominant alleles (of a possible 34), with a further 10 low-level alleles, suggesting DNA from other people who had handled the packaging.

The research showed that it is possible to generate usable DNA profiles from fingermarks alone, and the process is quicker and lower-cost because of the lack of an extraction step. Further work is needed, but the technique could potentially be incorporated into working forensic science laboratories.

Source: BioTechniques

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