Basic principles of real-time PCR

The three main categories of hybridization probes for real-time PCR are (1) cleavage based assays such as TaqMan, (2) displaceable probe assays such as Molecular Beacons and (3) probes which are incorporated directly into primers such as Scorpions. 

The use of Ct values also expands the dynamic range of quantitation because data are collected for every PCR cycle. A linear relationship between Ct and initial DNA amount has been demonstrated over flve orders of magnitude, compared with the one or two orders of magnitude typically observed with an endpoint assay. 

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