 Before the use of Taq polymerase, DNA polymerase had to be manually added every cycle, which was a tedious and costly process.Applications of the technique include DNA cloning for sequencing, gene cloning and manipulation, gene mutagenesis; construction of DNA-based phylogenies, or functional analysis of genes; diagnosis and monitoring of hereditary diseases; amplification of ancient DNA; analysis of genetic fingerprints for DNA profiling (for example, in forensic science and parentage testing); and detection of pathogens in nucleic acid tests for the diagnosis of infectious diseases.PCR amplifies a specific region of a DNA strand (the DNA target).