PCR is a common method of creating copies of specific fragments of DNA using thermostable DNA polymerases. Starting from very low amounts (ng range) of DNA templates, millions of copies of the target DNA fragment are produced within few hours. A typical PCR cycle consists of three temprature-controlled steps. In the first step, DNA template is made single stranded by raising the temperature to 94oC (Denaturation step). The second step involves lowering of temperature to 40-60oC so that the primers can anneal to the target sequence on the template DNA (Annealing step). The third step (Elongation step) is performed at 72oC, the optimal temperature for thermostable polymerases. The polymerase extends 3’end of each primer towards the other primer, and this results in complete replication of the target fragment. To amplify the amplicon by a factor of more than a million this cycle is repeated 25-30 times.

There is no limit to the applications of PCR. Most of the DNA based molecular markers are detected with the help of PCR including-

• RAPD
• AFLP
• ISSR
• STMS
• SAMPL