Fig. 1.

Schematic representation of the polymerase chain reaction (PCR). DNA (a) in the test sample is heated to separate the two strands (b). The reaction is cooled to allow primer (short bold lines) annealing to the target DNA (c), then heated again to allow addition of nucleotides to extend the nascent DNA molecule (d). At the end of the cycle, the target DNA has been duplicated (e). Each new DNA can then itself be a targeted molecule for the next cycle of amplification. The process is repeated for 25–40 cycles, and then products are visualized following gel electrophoresis (f). The left hand lane represents DNA markers of a known size against which the size of the amplicons is measured.