In real-time PCR, it is possible to measure the amount of PCR product at any time point. During the exponential phase in real-time PCR experiments, a cycle threshold (Ct) is determined at which point the fluorescence signal generated from a sample is significantly greater than background fluorescence. These Ct values are directly proportionate to the amount of starting template and are the basis for calculating mRNA expression levels or DNA copy number measurements. The quantification of the PCR product at specific cycle numbers allows complete understanding of the PCR process with truly quantitative estimations.
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