Describe the principle of Polymerase Chain Reaction (PCR) and its application in laboratory setting.

Polymerase Chain Reaction is an in vitro method used to amplify DNA fragments. It consists of three main steps, which are: (1) denaturing, (2) annealing, (3) and extension. During denaturation, the double-stranded DNA unwinds and is separated into single-stranded DNA strands. These strands serve as DNA templates, whereby designed primers bind (anneal) to complementary base pairs and flank specific sequence of the DNA. Subsequently, an enzyme called DNA polymerase catalyses the synthesis of specific DNA sequences from the template to create a double-stranded DNA. These steps constitute only one PCR cycle, which is repeated again for another 20-35 cycles to generate many more DNA fragments.