Faking DNA

August 18, 2009

Anyone who watches CSI, NCIS, or any of the many other crime shows on (US) network television will be familiar with the concept of DNA evidence.  Not just on TV, but in real criminal investigations, DNA evidence has been regarded as the “gold standard”.  In some cases it has irrefutably placed a suspect at a crime scene; in other cases, the use of DNA evidence and analysis that was not previously available has demonstrated the innocence of someone wrongly convicted of a crime. Basically, a DNA test starts with a small sample of genetic material; that sample is then “grown” in size by carrying out a procedure through which the DNA is replicated.  This generates enough DNA that its genetic code can be sequenced.  A comparison is then made among several regions of so-called “junk” DNA.  These sequences are not believed to have any genetic significance in humans, and thus should be subject to random mutations; if long enough sequences are compared, the likelihood of a match by chance is very small.

That is the theory, at least.  The New York Times has a report that a group of Israeli scientists has demonstrated the feasibility of producing “counterfeit” DNA, in a test tube, mimicking that of a selected person, such that currently used tests cannot distinguish between the counterfeit and the real thing.  In a paper [abstract] to be published in the journal FSI Genetics, the authors describe two experiments in which they made fake DNA.  In the first, they start with an actual biological sample containing a person’s DNA; in the second, they use a previously determined DNA sequence from a data base:

The scientists fabricated blood and saliva samples containing DNA from a person other than the donor of the blood and saliva. They also showed that if they had access to a DNA profile in a database, they could construct a sample of DNA to match that profile without obtaining any tissue from that person.

They found that these sample would match their target when subjected to a routine DNA analysis, without any noticeable anomalies.   Assuming their result holds up, this means that faking DNA evidence at a crime scene, or for other purposes, could be done fairly easily.  From the abstract:

It turns out that standard molecular biology techniques such as PCR, molecular cloning, and recently developed whole genome amplification (WGA), enable anyone with basic equipment and know-how to produce practically unlimited amounts of in vitro synthesized (artificial) DNA with any desired genetic profile. This artificial DNA can then be applied to surfaces of objects or incorporated into genuine human tissues and planted in crime scenes.

These techniques do require some specialized knowledge and equipment, but probably nothing that could not be found in a typical university laboratory.

The researchers, three of whom are associated with the Israeli company Nucleix Ltd, also claim to have developed a test that can distinguish between artificially produced DNA and natural DNA.  The test relies on the observation that, in natural DNA, some genetic loci are methylated, whereas artificial DNA there is no methylation.

It will be interesting to see if there is any follow-on to this research.  But it once again suggests that jumping to the conclusion that any forensic technique works infallibly is a Real Bad Idea.

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