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DNA technology is so much a part of the language of those speaking of crime detection, it is hard to believe it was first used to solve a crime in 1986. It allows any type of organism to be identified by the examination of DNA sequences that are identical to that species.
New methods of DNA technologies are being used in exciting ways, and previously unsuitable casework samples are now able to be tested. Detectives are finding it is important to keep up with DNA technology to know when to resubmit evidence that might previously not have yielded any results or to test items that had stains that were too small or degraded originally.
Useable DNA is being obtained from smaller and more unlikely sources, and cold cases may hinge on going back through the evidence and finding overlooked material from which a sample may be obtained. A toothbrush, stamp, or bite wound can yield a usable saliva sample. Patricia Cornwell used 100-year old saliva on the back of a stamp in her quest to identify Jack the Ripper. A single drop of blood or a single hair follicle may be enough to match to a perpetrator.
Previously, the bigger the DNA sample, the better. When DNA was first used, it was necessary to obtain a much larger sample, and the sample was often used up with the older DNA testing, called RFLP or Restriction Fragment Length Polymorphism. RFLP was one of the first types of DNA analysis in forensic investigation. With newer, more efficient techniques, RFLP is no longer used because of it requiring relatively larger amounts of DNA and because samples degraded by environmental factors, such as heat or mold, did not work well with RFLP.
Short Tandem Repeat
Current DNA testing is anchored by Short Tandem Repeat (STR) technology, which is the primary type of analysis currently being used. It is part of a larger type of analysis, PCR Analysis or Polymerase chain reaction (PCR), which can make millions of exact copies of DNA from a biological sample. This DNA amplification allows DNA analysis on biological samples as small as a few skin cells. To show some perspective, with RFLP, those DNA samples would have to been about the size of a...