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DNA Typing by RFLP Analysis

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DNA typing was introduced into forensic science in the mid 1980s, arising from discoveries made in biomedical research.  Ray White, an American geneticist at the University of Utah, identified regions of DNA that did not code for proteins but were highly variable between individuals.

Early research included the use of restriction enzymes to cut strands of DNA at specific locations and produce DNA fragments of defined lengths.  White separated the fragments based on size, calling the variations restriction fragment length polymorphisms (RFLP). In 1980, White and colleaguesdescribed the first polymorphic RFLP marker and proposed methods for mapping the human genome based on RFLP technology.01

Sir Alec JeffreysThe first forensic science applications of the technique arose from the work of Alec Jeffreys who found that RFLP technology could be used to develop patterns of restricted DNA that were more or less specific to an individual.  At the time, his work focused on paternity testing. In 1985, the British police from West Midlands approached Jeffreys to assist them in a rape-homicide case. Jeffrey’s work resulted in the release of a wrongfully convicted man and the apprehension and conviction of the true perpetrator. Soon thereafter, RFLP DNA evidence contributed to the convictions of Tommy Lee Andrews in Florida and Timothy Wilson Spencer in Virginia.02

The pieces of DNA cut by the restriction enzymes contain genes and non-coding DNA.  The non-coding DNA includes regions consisting of direct repeats of the same sequence of bases, referred to as tandem repeats.  The number of repeats of the sequence is genetically determined and, provided that the sequence is long enough and is repeated a sufficient number of times, will affect the length of the restriction fragment.  These regions are called variable number of tandem repeats (VNTR) loci.

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NOTE TO USERS: The President’s DNA Initiative DNA Analyst Training program and assessment were completed and published in 2005, in cooperation with the National Institute of Justice. The science and techniques in the program are sound and proven, however, program content has not been updated to include tools and technologies developed and in use after 2005, including many kits and robots. Assessment questions address only content delivered in this program and may not contain the full range of tools in use in your laboratory.