It has been in use in various scientific fields since 1983.
Amplification doubles with each step of the process.
When complete, scientists can separate the DNA fragments and determine the code at various loci. PCR is a technique used in multiplex systems in which several areas of interest, or loci, are amplified at one time. Each locus that is marked for testing requires its own optimal temperature for amplification. By using repeated chemical reactions in which the strands of DNA bind together and come apart using one compromise temperature, multiplex systems are able to amplify the DNA at more than one loci at the same time. By examining the gene sequence on a specific location on a chromosome and comparing the length with the gene sequence on the same chromosome from a different person, scientists can use the length differences to tell who left the sample.