Polymerase chain reaction (PCR), known as "DNA photocopying", is a technique used to replicate DNA segments quickly and accurately. This short animation of PCR demonstrates PCR principle.

PCR has numerous applications, such as in medicine (to detect low viral load), in forensic analysis (DNA fingerprinting), in molecular biology and in countless other fields.

Nonetheless, although these applications have driven the growth of the PCR market, PCR was limited in its quantification abilities and thus real-time PCR was invented.

In the descendant technology, the real-time PCR known also as real-time quantitative PCR (qPCR), the amount of accumulating DNA is detected and monitored by fluorescent dyes or probes during the reaction. This results in a typical sigmoid curve, enabling precise quantification of DNA, as illustrated above: