The three-step PCR process, or polymerase chain reaction, is used to amplify or copy DNA sequences. First, the two strands of DNA separate. Second, RNA primers anneal or attach to the DNA. Third, heat stable polymerase copies the DNA sequence.
These three steps can be repeated many times, yielding millions of copies of a DNA sequence in a few hours. Because the number of DNA copies increases exponentially with each cycle (2 to 4 to 8 to 16 and so on), the PCR process is described as a chain reaction. Today PCR is routinely used in paternity tests and forensic investigations.