PCR: Replicating success
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PCR often gets taken for granted, but there are ways of making it faster, more accurate and easier to perform. Pete Moore investigates. As a means of rapidly copying a selected template sequence from a DNA mixture in vitro, PCR by itself and in combination with other techniques has found a vast range of applications. These range from sequence detection and isolation for research, forensics and species identification to detecting mutations and polymorphisms and amplifying RNA-derived cDNAs for microarray analysis of gene expression. As well as standard PCR, the technique now comes in the form of real-time quantitative PCR (real-time PCR or qPCR). This uses fluorescent probes to monitor the amount of product at the end of each cycle, and real-time PCR machines look for the cycle at which they can first detect fluorescence. This relates to the number of copies of original template — the greater the number of starting copies, the fewer cycles are needed to reach fluorescence detection.