Deoxyribonucleic Acid (DNA) reveals an individuals unique genetic code, something very helpful to reveal clues in various crimes around the world. By recovering DNA from a crime scene, technicians can perform various tests to compare and analyze the DNA sequence. Among these tests are Gel Electrophoresis, the Sanger Method, and Southern Blotting.
             DNA can be extracted from almost any human tissue. Sources of DNA found at a crime scene might include blood, seamen, tissue from deceased victim, cells in a hair follicle, and even saliva. DNA extracted from items of evidence is compared to DNA extracted from reference samples from known individuals, normally from blood. Extracted DNA is treated with restriction endonuclease, which is an enzyme that will cut double stranded DNA whenever a specific DNA sequence occurs. The enzyme most commonly used in forensic DNA analysis is HaeIII, which cutes DNA at the sequence 5'-GGCC-3'. Following DNA digestion, the resulting DNA fragments are separated by size via electrophoresis in agarose gels (The Biology Project 1).
             Gel electrophoresis is used to distinguish between samples of genetic material. Because DNA is a charged molecule, it will move when an electrical field is applied to a liquid in which they are dissolved. Under this method, mixtures of nucleic acids or proteins are placed in wells near one end of a thin slab of a polymeric gel. Supported by glass plates, the gel is bathed in an aqueous or polyacrylamide solution (depending on the size of molecules to be separated) (DNA Techniques 1). Voltage is applied to both ends through electrodes. The DNA molecules then start moving across the solution from some initial small volume, that is, from essentially the same starting point, then the molecules can move at perceptibly different speeds. Usually smaller DNA molecules move faster than larger ones (Fairfiled 1). DNA molecules have negative charged phosphate groups, s...