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Cycle of quantification/qualification (Cq) is a parameter used in real-time polymerase chain reaction techniques, indicating the cycle number where a PCR amplification curve meets a predefined mathematical criterion. A Cq may be used for quantification of the target sequence or to determine whether the target sequence is present or not.
Two criteria to determine the Cq are used by different thermocyclers:
threshold cycle (Ct) is the number of cycles required for the fluorescent signal to cross a given value threshold. Usually, the threshold is set above the baseline, about 10 times the
Cycle of quantification/qualification (Cq) is a parameter used in real-time polymerase chain reaction techniques, indicating the cycle number where a PCR amplification curve meets a predefined mathematical criterion. A Cq may be used for quantification of the target sequence or to determine whether the target sequence is present or not.
Two criteria to determine the Cq are used by different thermocyclers:
threshold cycle (Ct) is the number of cycles required for the fluorescent signal to cross a given value threshold. Usually, the threshold is set above the baseline, about 10 times the standard deviation
In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, while ...
of the noise of the baseline, to avoid random effects on the Ct. However, the threshold shouldn't be set much higher than that to avoid reduced reproducibility due to uncontrolled factors.
Crossing point (Cp) and Take off point (TOP) are the cycle value of the maximum second derivative of the amplification curve.
References
Molecular biology Laboratory techniques Polymerase chain reaction Real-time technology {{Biology-stub