DNA extraction and quantification - An Introduction to Forensic Genetics - page 49

Plateau phase

High template

Low template

Exponential phase

Cycle threshold value (C T )

No template

20 30

10

Cycle number

Figure 4.10 Real-time PCR quantification. The schematic diagram shows the results from four
different template concentrations: high ( ), medium ( ), low ( ) and no template ( ).
As the PCR cycles the amount of fluorescence generated increases and each sample that contains
template will enter an exponential phase; as the reagents become exhausted each reaction will
enter a plateau phase. The cycle threshold value (C T ) is set to detect the point at which the
reaction has entered the exponential phase; the cycle number that this occurs will depend on the
amount of template DNA added. To determine the concentration of a DNA extract the C T value is
compared to the C T values from a range of standards

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