Which of the following process helps to ascertain the specificity of amplification in the case of realtime PCR technique?
Show Hint
Always run a melt curve analysis when using SYBR Green qPCR.
A clean, single peak confirms that your assay did not amplify non-specific targets or generate primer-dimers, validating your quantitative data.
Step 1: Understanding the Concept:
In real-time PCR (quantitative PCR qPCR), double-stranded DNA-binding dyes (such as SYBR Green) bind non-specifically to any double-stranded DNA produced during the reaction, including non-specific products and primer-dimers.
Therefore, a post-amplification method is required to verify that only the single, desired target gene was amplified. Detailed Explanation:
- Melt Curve Analysis (D): After the PCR cycles are complete, the reaction mixture is slowly heated from a low temperature (e.g., $65^\circ\text{C}$) to a high temperature (e.g., $95^\circ\text{C}$) while monitoring fluorescence.
- As the temperature rises, double-stranded DNA denatures into single strands, causing the intercalated fluorescent dye to release and the fluorescence signal to drop rapidly.
- The temperature at which $50\%$ of a specific DNA product denatures is its melting temperature ($T_m$), which depends on its length and GC content.
- Plotting the negative derivative of fluorescence over temperature ($-\text{d}F/\text{d}T$ vs. Temperature) yields distinct peaks:
- A single, sharp peak indicates a single, highly specific PCR product.
- Multiple peaks indicate the presence of non-specific products or primer-dimers.
- Cycle threshold ($C_t$) (A) is used for quantification, not specificity.
- Amplification associated fluorescence (C) measures product accumulation, not product identity or specificity. Step 2: Final Answer:
Melt curve analysis is used to determine the specificity of amplification in real-time PCR, corresponding to option (D).
