Yes, yes, May is a distant memory… but that’s okay. Remember how cold and wet it was? Now you can enjoy this recap from the balmy confines of July. 🙂
This Dinner was another one that was packed to the rafters, which was really gratifying to see. When you book people who cover your own interests, you do kinda hope that other people will geek out as much as you will. Aside from being thoroughly educational and entertaining, I’ve got to say it turned out to kinda accidentally be one of the bawdiest evenings we’ve had. I’ll do my best to get through this recap with as few mentions of semen as possible…
Valerie is a forensic biologist and President and Co-founder of Wyndham Forensic Group in Guelph. Her educational background is in biology, with an Hons. B.Sc. in Biology from the University of Guelph and a M.Sc. in Molecular Biology from McMaster University. She started her career at the Centre of Forensic Sciences in Toronto, and founded Wyndham Forensic Group in 2009.
Generally, forensics is: “The application of science to answer questions of interest to the legal system”. Thanks to shows like CSI, many of us are familiar with a variety of branches of forensics — toxicology, ballistics, hair and fibre analysis, even forensic accounting. Valerie’s work, however, focuses on the biological, the traces we all leave behind in all of our environments.
Forensic biology deals with both physiological and behavioural evidence. Physiological including things like fingerprints and DNA analysis, and behavioural including things like voice prints and handwriting analysis. DNA work is one of the mainstays of Valerie’s lab.
DNA fingerprinting was first developed in 1984-85 in the UK by Sir Alec Jeffreys of Leicester University. DNA analysis doesn’t involve comparing the entire “code” of different people, but variability along certain specific locations. No two people (except identical twins, though there’s some new research there, too) have exactly the same DNA, so there are always differences to be found. DNA can be gleaned from blood, semen, saliva, hair shaft vs. root, bone, teeth, and skin cells.
Around the same time scientists developed a technique called polymerase chain reaction (PCR) that made DNA analysis much easier. Copies of DNA could be made much more expediently in a test tube. It did, however, take a number of years before this technique was widely adopted in forensic science.
The use of DNA evidence in criminal trials had a bit of an uneven start in the late 1980s. Private companies initially did the testing, and a number of cases were prosecuted successfully, but a major challenge was brought forth in New York v. Castro and the evidence was ruled inadmissible.
The FBI started doing forensic DNA analysis in the late 1980s, and Canadian labs followed suit soon after. In 1995 Bill C-104 was passed in Canada, allowing judges to order “DNA Warrants” so police could obtain biological samples from people to enable comparisons of their DNA profiles with crime scene samples. These samples could be taken by cheek swab, blood, or other means, and police don’t necessarily have to be terribly polite about getting them.
The National DNA Databank was implemented in Canada in 2000, enabling wide scale comparisons of crime scene DNA profiles with profiles of known offenders. Various organizations all share access to the Databank, which is managed by the RCMP.
So, with that bit of background on how we got to where we are today with the use of DNA analysis in the public and private sectors, Valerie embarked on a case study, comparing the real world with shows like CSI. We had an imaginary murder victim and crime scene, which would be cordoned off much more stringently than on TV, and “worked” by suited, masked, and gloved CSI workers. Nobody’s showing up in a tank top with their hair flowing free.
Evidence, including biological samples (which may contain DNA) obtained at a crime scene go through a number of potential procedures along a timeline:
- Exam Strategy
- Biological Screening
- DNA Analysis
- DNA Databank
As an interesting note, forensic scientists can be called to testify by both the prosecution and the defence in court cases.
Next Valerie did a bit of a photographic comparison of how the lab works (and doesn’t work, in the case of CSI). Paperwork and tests are not run right next to each other. Equipment used in testing doesn’t just sit out where cross-contamination can take place, and again, no tank tops or loose hair in the lab.
She talked a bit about how ultraviolet light is used to analysis potential biological deposits on materials. This was one section of the presentation where semen came up a lot.
Back to our collected evidence! Valerie discussed how various types of evidence are gathered, kept from becoming contaminated, and how they would be analyzed. In this case, a pair of bloody jeans, internal and external swabs from the victim’s body, fingernail clippings from the victim (skin cells and other things can get stuck under nails), a knife found near the scene, and a Tim Hortons cup found near the scene. (Which could be nothing or could have a sample of the killer’s DNA.)
As we mentioned earlier, everyone’s DNA is at least a little different. So what DNA analysis provides is what is known as the absolute power to exclude, i.e. your DNA does not match this crime scene sample, so you weren’t at the crime scene. Now, does that mean that DNA can unequivocally finger the guilty? Not exactly. It provides what is known as the increasing power to include (or identify).
Now, most of people’s DNA is identical. We are all pretty much programmed to be bipedal with two arms, two legs, two eyes, some hair, etc. Humans even share nearly 99% of their DNA with chimps, so the differences among people are, overall, pretty small. But scientists know what parts of human DNA are variable, and it’s those that they amplify with PCR and analyze.
That means that if the DNA analysis of a suspect is a match to a crime scene sample, that person cannot be excluded as the possible perpetrator, but cannot be said with 100% certainty to be the killer. Now, the likelihood of the killer being someone else with the same DNA sequence could be quadrillions to one, but scientists are very specific and careful people. 🙂
Forensic scientists who testify in court also tend to be well trained in clearly explaining what DNA results mean, since, depending which side they’re testifying for, the other would likely jump at the chance to discredit too black and white a statement about DNA evidence.
Now, as a law enforcement technique, DNA analysis is fairly new. After all, fingerprints had been used by the police since the 1800s. So where is it going as a science?
Research is being done to speed up development of DNA profiles — ideally they could be done right at a crime scene using a “lab on a chip”. Those profiles could be instantly compared in the field to known profiles in the National Databank.
DNA analysis is also going more mainstream. It’s being used to predict ancestry and phenotypic characteristics, which can be relevant to everything from forensic anthropology on old specimens to determining paternity. Companies like 23andMe do DNA analysis for the public, and in addition to telling you basic things like likely hair and eye colour, they can also tell you about disease risks, even how much Neanderthal DNA you have (me: 2.4%).
These types of tests becoming cheaper and more accessible can be a slippery slope. For example, rates of “unexpected paternity” are estimated at between 1 and 30% depending on the segment of the population profiled.
And with that, Valerie concluded her talk and we moved on to an extensive and lively Q&A. We want to thank Valerie again for a fascinating presentation and answering many, many questions, ranging from uses of DNA evidence in court to recommended education and job prospects for those interested in forensics.
As always, we’re taking the summer off, but we hope you’ll join us again in September for our new season of Girl Geek Dinners.