Question

The copy number of an expressed gene is measured by

• A. Touchdown PCR
• B. Reverse transcriptase PCR
• C. Inverse PCR
• D. Realtime PCR

Hint:

PCR Variations:
Real-Time PCR (qPCR) $\rightarrow$ Gene copy number & expression quantification.
RT-PCR $\rightarrow$ Amplifies RNA into cDNA.
Inverse PCR $\rightarrow$ Unknown flanking regions.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Quantitative Real-Time PCR (qPCR RT-qPCR) measures target nucleic acid copy numbers and gene expression levels in real time using fluorogenic chemistry.
Key Formula or Approach:
\[ C_t \propto -\log_2(\text{Initial Target Copy Number}) \]

Step 2: Detailed Explanation:
Comparing PCR methodologies:
1. Real-Time Quantitative PCR (qPCR RT-qPCR): Monitors the exponential amplification of cDNA/DNA during each cycle using fluorescent reporter dyes (SYBR Green, TaqMan probes). The cycle threshold ($C_t$) is inversely proportional to the log of the initial template copy number, enabling exact absolute and relative quantification of expressed mRNA transcripts.
2. Touchdown PCR: Optimizes primer annealing specificity.
3. Inverse PCR: Amplifies unknown sequences flanking a known region.

Step 3: Final Answer:
Therefore, copy number of an expressed gene is measured by Realtime PCR, corresponding to option (D).