The polymerase chain reaction (PCR) is an artificial method of the gene amplification by which several copies of the desired DNA segment can be obtained in a short period. This technique was developed by Kary Mullis in 1985. This technique is based on a principle that the DNA undergoes denaturation at high temperature. Selectable markers are used to select for successful transformants from untransformed cells. The ampicillin resistant gene in the plasmid is one of the example of this.