DNA research. Preparation of a process cell for the amplification of DNA fragments by polymerase chain reaction (PCR). PCR is used where only a tiny amount of DNA may be obtained, for example in forensic science. The DNA from an electrophoresis gel may be split into single strands, the two complimentary strands being resynthesised using DNA polymerase and labelled nucleoside triphosphates. If this process is repeated many times, a large number of duplicates of the original fragment may be produced.