Real-time quantitative PCR (qRT-PCR) is used to quantify mRNA expression levels. In this technique, cDNA is first synthesized from mRNA using reverse transcriptase. The SYBR Green method detects PCR product by binding to double-stranded DNA. A fundamental limitation of SYBR Green compared to TaqMan probe-based detection is:
- A SYBR Green requires radioactive labeling for detection
- B SYBR Green probes are cleaved during PCR, releasing signal proportional to product
- C SYBR Green cannot be used in multiplex PCR for simultaneous detection of multiple targets because it fluoresces with any double-stranded DNA, including primer dimers and non-specific products ✓
- D SYBR Green only works with RNA templates and cannot detect genomic DNA
Explanation
SYBR Green intercalates into all double-stranded DNA indiscriminately; any PCR product, including primer dimers and non-specific amplicons, generates fluorescent signal, reducing specificity. Melt curve analysis post-amplification is required to confirm product identity. TaqMan probes (sequence-specific fluorescent-quencher oligonucleotides cleaved by Taq polymerase 5'→3' exonuclease activity during extension) are inherently more specific because signal is only generated when the probe hybridizes to its exact target sequence. TaqMan-based multiplexing uses probes with different fluorophores to simultaneously quantify multiple targets in a single reaction.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.