PCR Techniques · Pathology

In Real-Time PCR (qPCR), what does the 'Ct' (cycle threshold) value represent?

  1. The total number of cycles in the PCR run
  2. The temperature at which the DNA denatures
  3. The cycle number at which fluorescence exceeds a defined background level
  4. The concentration of magnesium ions required for the reaction
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Correct answer: The cycle number at which fluorescence exceeds a defined background level

The Ct value is inversely proportional to the amount of target nucleic acid in the sample. A lower Ct value indicates a higher starting concentration of the target DNA template.

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