Section 3: Genetics, Cellular and Molecular Biology
Recombinant DNA technology
Subtopic: Fundamentals of Recombinant DNA technology
Question Statement:
A proto-oncogene is suspected to have undergone duplication in a certain type of cancer. Of the
following techniques, which one would verify the gene duplication?
Options:
(A) Northern blotting
(B) Southern blotting
(C) South western blotting
(D) Western blotting
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.19)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Recombinant DNA Technology / Molecular Biology (Blotting Techniques & Gene Copy Number)
**2. Detailed Step-by-Step Analysis**:
- The question asks which technique can verify a **gene duplication event** (an increase in the genomic DNA copy number of a suspected proto-oncogene, such as *MYC* or *HER2/neu*).
- Let us compare the targets and capabilities of blotting techniques:
- **Southern blotting**: Uses labeled DNA or RNA probes to detect specific **DNA sequences** and determine gene copy number, restriction fragment length polymorphisms, and genomic structural rearrangements (such as duplications, insertions, and deletions) in digested genomic DNA. A doubled signal intensity relative to a single-copy internal reference gene confirms gene duplication.
- **Northern blotting**: Analyzes **mRNA** expression levels, but elevated mRNA expression could result from transcriptional upregulation rather than a physical DNA gene duplication.
- **Western blotting**: Analyzes **protein** abundance, not gene copy number.
- **Southwestern blotting**: Studies **DNA-protein interactions** using labeled DNA probes against immobilized nuclear proteins.
- Therefore, **Southern blotting** is the definitive hybridization technique to verify gene duplication at the genomic DNA level.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Northern blotting measures RNA transcript abundance, not genomic DNA copy number.
- **Option (B) [CORRECT]**: Southern blotting directly measures genomic DNA copy number and confirms gene duplication events.
- **Option (C) [INCORRECT]**: Southwestern blotting investigates DNA-binding proteins.
- **Option (D) [INCORRECT]**: Western blotting measures protein translation levels.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **B**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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