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Kary Mullis developed the technique of the polymerase chain reaction (PCR) in 1983. He won a Nobel Prize for the procedure in 1993 as it became quite clear PCR had revolutionized the worlds of biochemistry and genetics. PCR enables researchers to amplify extremely small samples of DNA, even one molecule, into virtually unlimited quantities. PCR is now a common laboratory procedure, and because of its broad range of applications, it is rapidly reaching the nonscientific community as well. For example, PCR is used in paternity testing. The genes of the father can be amplified and compared to the childís DNA for similarities. Courts are also using PCR to compare genetic evidence found at a crime scene to that of a suspectís DNA. This usage enables even the smallest amount of DNA to act as a witness to the crime allowing a greater resolution between guilt and innocence. The process of PCR occurs in three steps: denaturing, annealing and extension. Each repetition of these steps constitutes one cycle and doubles the amount of DNA present in the sample. Each of these steps is conveniently triggered by temperature. Temperature regulation enables the ingredients for each step to be mixed in the same container. All the researchers need do is mix up the recipe. The raising and lowering of the temperature does the rest.

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