Polymerase chain reaction (PCR) is a widely used method for making copies of DNA. PCR involves the repeated heating and cooling of a DNA sample in the presence of specific primers, which are short pieces of DNA that bind to the ends of the DNA region of interest. During the heating step, the DNA strands separate, and during the cooling step, the primers bind to the ends of the DNA strands. A DNA polymerase enzyme extends the primers, adding nucleotides to them until the DNA region of interest is copied. This process is repeated for many cycles, resulting in exponential amplification of the DNA region of interest. PCR is a powerful tool that is used in many different applications, including medical diagnostics, forensic analysis, and DNA research.