This week I want to discuss some of the sources I’ve not found useful for fiction. The best place to start discussing sources for mystery writing is do NOT use television. A seminar at our local “Croak and Dagger” chapter of Sisters in Crime pointed to a few of the most glaring errors: Forensic scientists are never as cute as actresses, almost never wear high heels, and never produce answers as fast as TV crime drama criminolgists.
Cute? You be the judge. High heels? May be important for actresses and may feel important for a very short woman, but not likely to be seen in any lab.
Speed of results? That is the big error. If you deliver a nanogram of material to a lab for DNA analysis, the first step is PCR, which increases the nanaogram of material so there is enough to be analyzed. I believe it works about the way living cells replicate DNA, to increase what is presented. Assuming I’m right, it doubles the DNA sample size. Still too small. So it keeps doubling the amount until you have enough. Twenty doublings and the nanogram is a microgram. Forty and you have a milligram, theoretically anyway. By the way, this is done in a thermal cycler.
The time required for each cycle has decreased but is often significant. A few days to do the PCR amplification is not unreasonable, though some labs with particularly modern equipment may be faster. But, many labs have old equipment and I’ve been told by one state lab that they only do the DNA analysis when the result is needed for trial.
So, if you’re writing crime fiction it may be much more interesting to make fun of the nonsense on CSI and force your detective to wait until the trail is colder. Or, more realistically, the detective doesn’t get the DNA results until the case is solved. Also, nothing in any technique avoids contamination problems. People breathe out nanograms of DNA with every breath. Sloppy handling will tend to invalidate any DNA analysis.