The purpose of PCR is to amplify small amounts of a DNA sequence of interest so it can be analyzed separately. PCR can be used to make a large amount of a specific piece of DNA or to test a DNA sample for that sequence.
PCR is used for research when it is necessary to make a large amount of a single gene, such as for genetic engineering or cloning. PCR is also used to test whether or not a particular gene product is present in a sample. In forensics, PCR technology is used to carry out DNA fingerprinting to analyze crime scene DNA evidence. PCR can also be used in medical settings to carry out tissue-typing for organ transplants.