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LEGAL REPORT: FORENSICS DNA Getting morefrom New technique cleans up samples, providing more evidence for investigators, but still needs peer review and validation from the courts. BY JE REMY HAINSWORTH "I ndigo is a bugger," says Derrill Prevett, a Nanaimo, B.C.-based prosecutor, talking about the prob- lems with extracting and analyzing DNA samples from evidence sources such as indigo-dyed fabrics like blue jeans. Such contamination is a problem that's plagued police and prosecutors since DNA made its debut in criminal casework in the United Kingdom in 1987 following the work of British genetics researcher Sir Alec Jeffreys. And Prevett knows what he's talk- ing about. With Cecilia Hageman and Wayne Murray, he's the author of the DNA Handbook for the legal profession. It was Prevett who stickhandled DNA evidence through the Robert Pickton serial-killing case that resulted in six convictions for second-degree murder in 2007. That case backlogged Canada's labs for months with more than 200,000 DNA samples flowing from the killer's Port Coquitlam, B.C. property. Now, however, there's a breakthrough from a University of British Columbia department of physics and astronomy research team that may remove that indigo problem as well as other contami- nation roadblocks to extracting usable evidentiary DNA. Those include humic acid from soil, melanin from hair sam- ples, and hematin from blood. All of those can co-extract with DNA. As such, in cases where there is insufficient DNA or co-extraction, it's estimated 10 per cent of crime scene samples may fail. The new method, say investigators and prosecutors, could provide better evidentiary samples for both police and court processes. "It's a great advancement for cleaning up and getting samples that in the past would be problematic," says Ron Fourney, RCMP director of forensic science and identification services. There are things that render a sample useless by degrading the DNA. "Bleach will do it, so will ultraviolet light. Things growing on it will do it," says Prevett. Further, Fourney is the first to admit the complexities of DNA forensic science are frequently a bit of a "twilight zone." DNA, or deoxyribonucleic acid, is a nucleic acid in a double-helix chain containing the genetic instructions used in the development and functioning of 38 NO VEMBER / DECEMBER 2009 www. C ANADIAN Law ye rmag.com all known living organisms and some viruses. Each human cell contains 23 base pairs of chromosomes, each con- taining close to 100,000 genes and DNA chains made up of 100 million base pairs of nucleotides. In short, the complete human genetic code is based on three bil- lion base pairs dictating everything from height to hair colour. In order to build a genetic fingerprint from a sample taken from a crime scene, forensic scientists need a clean sample which is then cut to produce samples of differing lengths. It's here that Prevett suggests the new process is interesting as a contaminant such as indigo can inhibit the chemical scissoring process for cutting the DNA strands. The segments are then sorted in a process called gel electrophoresis. Short segments move faster than long ones in the electrified process which allows for sorting. The resulting sequences are then transferred to a nylon membrane and identified according to the code they contain using radioactive markers. The result is a series of bars known as short tandem repeats. And, just as a barcode identifies a specific product, so does a BRANDON STEEN