Restriction fragment length polymorphisms
Restriction fragment length polymorphisms (Forensic Science)
Restriction fragment length polymorphisms (RFLPs) were the first DNA (deoxyribonucleic acid) typing to be used as forensic evidence. English geneticist Alec Jeffreys and his colleagues identified DNA fingerprints for forensic application in 1985. They examined regions of the human genome called minisatellites, which are made of a DNA sequence that is tandemly (end-to-end) repeated hundreds of times. These are also called variable number of tandem repeats (VNTRs). Individuals vary in the numbers of tandem repeats of that DNA sequence they have in their genomes.
In detecting these RFLPs, DNA is isolated from cells. A restriction enzyme (which makes sequence-specific cuts in DNA) is used to cut outside the repeating sequence. DNA is separated based on size through the use of gel electrophoresis. The DNA fragments are transferred from the gel to a membrane (called a Southern blot). A single-stranded, labeled DNA probe complementary to the repeating sequence is hybridized with the DNA on the membrane. The probe base-pairs with its complementary sequences on the membrane. This labeled probe allows the VNTR regions to be detected among all the DNA in the genome. The size of the fragment detected varies depending on the number of tandem repeats the individual has. This is length polymophism—length variation from individual to individual.
Samples of blood, semen, saliva, or other biological materials are often collected at crime scenes for...
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Further Reading (Forensic Science)
Fisher, Barry A. J. Techniques of Crime Scene Investigation. 7th ed. Boca Raton, Fla.: CRC Press, 2004.
Gill, Peter, Alec J. Jeffreys, and David J. Werrett. “Forensic Application of DNA ’Fingerprints.’” Nature 318 (1985): 577-579.
Jones, Phillip. “DNA Forensics: From RFLP to PCR-STR and Beyond.” Forensic Magazine, Fall, 2004.
Rudin, Norah, and Keith Inman. An Introduction to Forensic DNA Analysis. 2d ed. Boca Raton, Fla.: CRC Press, 2002.
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