A thermal cycler is an electronic temperature control device used to automate the polymerase chain reaction. The machine consists of a control system, a block which holds the reaction tubes, and a heating/cooling system. In some early models the temperature control was acheived using a fan and an electric heater. More recent cyclers use a Peltier element (a compact solid-state heat pump) which is much more reliable and can actually cool samples below the ambient temperature.

Briefly, the polymerase chain reaction involves timed heating/cooling of the DNA and Taq DNA polymerase to achieve exponential amplification of a specific DNA sequence. The thermal cycler does this automatically. It's a far superior system to a graduate student with three water baths, a stopwatch, and three hours to kill.

The polymerase chain reaction was initially patented by Cetus Corporation, and thus anybody using it in research has to buy a licence. Fortunately, any laboratory buying a thermal cycler is also buying a licence, included in the (expensive) purchase price of the machine. Originally, cyclers were only available through Perkin-Elmer, but now many companies sell them.

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