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Standard gel electrophoresis techniques for separation of DNA molecules provided huge advantages...

Standard gel electrophoresis techniques for separation of DNA molecules provided huge advantages for molecular biology research. However, many limitations existed with the standard protocol in that it was unable to separate very large molecules of DNA effectively. DNA molecules larger than 15-20kb migrating through a gel will essentially move together in a size-independent manner. At Columbia University in 1984, Schwartz and Cantor developed a variation on the standard protocol by introducing an alternating voltage gradient to better the resolution of larger molecules. This technique became known as Pulsed Field Gel Electrophoresis (PFGE). The development of PFGE expanded the range of resolution for DNA fragments by as much as 2 orders of magnitude. The procedure for this technique is relatively similar to performing a standard gel electrophoresis except that instead of constantly running the voltage in one direction, the voltage is periodically switched among three directions; one that runs through the central axis of the gel and two that run at an angle of 120 degrees either side. The pulse times are equal for each direction resulting in a net forward migration of the DNA. For