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LITTLE KNOWN ASPECTS OF DNA ANALYSIS

© Elizabeth Becka Lansky

DNA is the current darling of forensic science, and not unreasonably so. It can exclude such a vast number of human beings that the odds of the perpetrator being anyone other than your suspect become astronomical. Any good murder mystery utilizing a grisly homicide will have bodily fluids and tissues floating about, necessitating the use of DNA analysis to solve the crime. However, instead of giving a dry textbook description of the process to add authenticity to your tale, consider writing a scene utilizing these factors:

Types of Analyses: PCR: Polymerase Chain Reaction. The result of this test is a 3/8 inch wide strip of paper with blue dots showing someone's type of each gene allele. Some alleles will have two different types, some will have three. If all three light up, the sample is either contaminated, decomposed, or a mixture, because you will only have two, one from Mom and one from Dad. A decomposed sample, contrary to what O.J.'s lawyers might tell you, will not come out looking like someone else's DNA. It will either look like no one, or everyone. This type of testing is partially automated and fast (used to be 1-2 days before you had to do a yield gel and all that junk, now it's closer to a week).

RFLP: Restriction Fragment-Length Polymorphism. This is the test that gives you the bar-code-like autorad. This analysis is extremely labor-intensive (the analytical gel has to run for 17 hours; you might have your hero return to the lab after hours just to shut it off). Any lab performing this type of analysis will be looking to change to the much faster, and more exclusionary, STRs. A lab which shall remain nameless was run by a person who had spent her entire adult life there, so that while she wanted to rule with an iron hand, she was extremely insecure. This caused her to shun professional meetings, organizations, and peers (who were disregarded because they were obviously trying to circumvent her ambitions) and invest in the expensive equipment and training for RFLP when anyone could have told her it was on its way out. As luck would have it, there was a sudden influx of money for a new building and equipment so that the taxpayers did not notice that within a year they had made another investment, in STR technology, and she kept her job. You never see scenarios like that in a mystery novel, but it's a very real concern to administrators who have to make a judgment call about where technology is going to go. (Who would have guessed the VHS vs Betamax thing?)

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