“End-point” vs “real-time” detection

The PCR products can be detected after the PCR is completed, usually for “qualitative” analysis (presence/absence of product), either by (gel) electrophoresis or Melting Curve analysis. Detection can also be done after each cycle, as PCR proceeds, using laser optics (i.e. in ‘real-time’). The amount of initial target cDNA in a reaction can then be very accurately related to how many amplification cycles are required for a product to appear. This is the basis for “quantitative” PCR (qPCR), which is extremely accurate over a wide range of target concentrations (see the BEEBOOK paper on molecular methods; Evans et al., 2013).