Polymerase chain reaction, or PCR, is a laboratory technique used to make multiple copies of a segment of DNA. This procedure is a man-made version of DNA replication. Using PCR it is possible to generate thousands to millions of copies of a particular section of DNA from a very small amount of DNA. Polymerase chain reaction allows the pieces of DNA to be amplified so they can be detected. Polymerase chain reaction may be used for certain changes in a gene or chromosome, which may find and diagnose a genetic condition or a disease, such as cancer.