The success of DNA based markers lead to the development of PCR. PCR (polymerase chain reaction) is a DNA amplification technique that can be applied to various types of fragments. Prior to this development, to amplify DNA, it had to be cloned or isolated. Shortly after the discovery of PCR came the idea of using PCR-based markers for gel electrophoresis. These type of markers are based on PCR primers and are categorized as DNA sequence polymorphism.