Mapping marijuana's DNA
The creation of a genetic database for cannabis is a
scientific first.
Image: iStockphoto

Professor Rod Peakall does not think highly of the science in CSI.

The procedural crime TV show uses the trappings of forensic investigation, he argues, but the execution usually falls short of the possible or firmly in the realms of the ridiculous.

“They pump someone’s stomach, and identify plant material from somewhere like the Everglades, and I think, ‘Come on, we can’t do that yet’.”

But if the show was to run an episode where cannabis DNA from different plants was compared to establish if they shared a common source, Peakall might pay closer attention.

The evolutionary biologist from the School of Botany and Zoology at ANU has been leading a team that compared the DNA of over 500 cannabis plants seized in drug raids from all over Australia.

The project was initially established by researcher Dr Simon Gilmore, the project was a collaboration between ANU, the Australian Federal Police (AFP) and the Canberra Institute of Technology, where Gilmore was teaching. The final phase of the project was completed by Dr Chris Howard.

It has resulted in a national cannabis genetic database which the AFP believes could be useful in breaking crime rings and identifying cannabis production sites.

Gilmore says he’d wanted to pursue a project in plant DNA analysis for some time before this idea stuck.

“I had heard that a project using DNA markers in cannabis had been conducted by Adrian Gibbs and his colleagues at the Research School of Biological Sciences at ANU. I took a proposal to the AFP, suggesting that the project be reopened using the new generation of DNA techniques that had recently become available.

“The AFP, through the agency of James Robertson, National Manager of Forensic and Data Centres, were extremely supportive and immediately provided some interim funding.”

Further funding for the project also came from the Australian Research Council, and the National Drug Law Enforcement Research Fund.

With its CSI overtones, the crime-fighting angle to the project is understandably attractive to the general public. But it’s the scientific ground broken in the creation of the database that has Peakall most excited.

“To our knowledge this is the first botanical forensic study which has followed human forensic guidelines, where applicable, to validate reproducibility of the methods in plant forensics,” he says.

“It’s a test case for forensic botany because we needed to know if the methods developed for humans were applicable for plants. We had a good sense that they would be, because we’ve been using similar methods in other areas.

“In a forensic context we had to go through a lot more validation, testing again and again for things that we might otherwise take for granted in other research projects. Is DNA inherited? How reproducible are DNA profiles? Do you get the same results every time?”

Before tackling these questions, the researchers had to get over one major hurdle – what’s the value of analysing the DNA of something that can be easily cloned?

When human DNA is analysed in a forensic context, it’s usually for the purposes of individualisation. Investigators try to determine what is genetically unique about a sample so that they can place a suspect or victim in a particular place, such as the crime scene.

Unlike humans, plants can be easily propagated. Anyone with a pair of secateurs and a growing medium can take a clipping and foster what’s effectively a genetic clone of the original plant.

This is both a blessing and a curse in a forensic context.

“Suppose there is a whole string of criminal consortia sharing hydroponic activities, but they would be seen in a drug bust to be independent,” Peakall says. “There is evidence that connects them, but it’s difficult for the police to find. If you find a series of genotypes or clones that are shared among these consortia, that may provide evidence of linkage.

“The problem of evidence for linkage is that just because you’re sharing a clone doesn’t mean you’re overtly conspiring. It might be that you happen to know the same crook who supplies everybody with it, or you bought that variety over the internet. If the police start to compile that DNA evidence with other lines of evidence, it suggests consortia, it adds to the case.”

But on the blessing side of the equation, it’s possible that you might turn up an unusual genotype, which has the capacity to link together a whole series of drug busts.

To find out if any of this was possible, the research team needed to apply human forensic analysis processes to extracting DNA from the plant samples.

“Significant work had to be done to show that the technology was reliable and accurate enough to be used in a forensic laboratory,” Gilmore recalls. “Although we had a lot of material to work through we had a very strong team and first class technical assistance, so we were confident of completing the work.”

Each sample needed to be frozen solid, then crushed into a fine powder. The researchers then used conventional forensic techniques to analyse parts of the DNA called short tandem repeat markers, which are areas where genetic individualisation is known to occur.

After months of work, the team were able to show that there was enough genetic variety in Australian cannabis strands to establish a working database.

“I’m extremely proud that we have been able to repay the investment by government and law enforcement, not only by developing a technology that has strong potential for investigating drug related crime, but also because we took the necessary extra steps to validate the technology so that it could be readily adopted by law enforcement,” Gilmore says.

“There are literally thousands of Honours and Phd studies worldwide that show the potential of particular methods for forensic investigation, but very few of these are actually validated and end up adopted by the forensic community.”

Peakall says the project has shown the potential for DNA profiling of large samples in a forensic botany context, and might have uses in the policing of other illicit crops like opium poppies. More importantly, in appropriate circumstances these DNA methods maybe applied to other botanical evidence.

If it’s picked up by law enforcement agencies in the US, there’s also a chance it could end up on a CSI episode. Maybe then the scientists would watch.

Editor's Note: A story provided by the ANU Reporter.  This article is under copyright; permission must be sought from Australian National University to reproduce it.