Polymerase chain reaction (PCR) is an extremely useful technique for specific in vitro amplification of nucleic acids and has a large number of applications. The utility of PCR comes from the very small amount of starting material required. Manipulation of the specificity can be achieved by simply varying length and nucleotide sequence of primers and annealing temperature. This can be of particular importance in medical diagnosis when an infectious agent is present in low numbers. PCR is also an important diagnostic tool for many genetic diseases and chimerism testing for bone marrow transplants. Furthermore, it has played a pivotal role in the analysis of microbial species, such as amplifying and sequencing 16S rRNA in order to understand the phylogenetic relationships among different bacterial species.
