Explain how polymerase chain reaction is used in DNA fingerprinting

DNA extracted from a crime scene is normally available in small quantities so PCR can be used to amplify this quantity to a reasonable concentration which can then be used to run a gel electrophoresis to identify an individual at the crime scene. PCR works as follows: Double stranded DNA is heated to around 90 degrees to break the hydrogen bonds holding opposite bases together. Single stranded DNA is then cooled to around 65 degrees. This allows for free floating DNA primers and DNA polymerases to synthesis double stranded DNA using the single strand as a template. The DNA primer is complementary to a small portion of DNA from the source. The DNA primer anneals to the target sequence and DNA polymerase synthesises the remaining sequence using free floating nucleotides creating double stranded DNA. This process is repeated until the DNA is available in sufficient concentrations.