Realtime PCR

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Realtime PCR (sometimes abbreviated rt-PCR, which is unfortunately readily confused with reverse-transcriptase PCR, also rt-PCR) is a method to quantitate the number of target genes in a DNA sample. In realtime PCR, the concentration of DNA product is continuously measured in the PCR machine, usually by the addition of SYBR green, a fluorescent dye that binds double-stranded DNA, and is fluorescent when bound to DNA. This fluorescence is measured during amplification with a fluorometer built into the PCR machine. In a realtime PCR run, the fluorescence increases more-or-less exponentially at first, then plateaus as the reagents are exhausted. Where each PCR reaction crosses some threshold (best set pretty low) can be plotted against a standard curve to determine the concentration of PCR target in the original sample.

Fig 1 from Yang et al. Virology Journal 2009 6:142