Which DNA fingerprinting technique uses variable number tandem repeats (VNTRs) and is based on Southern blot hybridization?

Explanation

## VNTR-Based DNA Fingerprinting **Key Point:** RFLP (Restriction Fragment Length Polymorphism) analysis using VNTRs was the first DNA fingerprinting technique developed by Alec Jeffreys in 1984. It detects polymorphisms in variable number tandem repeat regions using restriction enzymes and Southern blot hybridization. ### Mechanism of RFLP-VNTR Fingerprinting 1. **DNA Extraction** from biological evidence (blood, semen, saliva) 2. **Restriction Enzyme Digestion** cuts DNA at specific recognition sites 3. **Gel Electrophoresis** separates DNA fragments by size 4. **Southern Blot Transfer** to nitrocellulose membrane 5. **Probe Hybridization** with labeled VNTR probes 6. **Autoradiography** visualizes banding pattern **High-Yield:** RFLPs using VNTRs produce a unique "DNA fingerprint" with 99.9% discrimination power in forensic cases. The banding pattern is individual-specific (except in identical twins). ### Comparison with Other DNA Techniques | Technique | Marker Type | Method | Advantages | Disadvantages | |-----------|-------------|--------|------------|---------------| | RFLP-VNTR | VNTRs (10–100 bp repeats) | Southern blot | Highly discriminatory | Time-consuming, requires intact DNA | | STR Analysis | Short tandem repeats (2–6 bp) | PCR-based | Fast, works with degraded DNA | Lower individual discrimination | | Microsatellites | Dinucleotide/trinucleotide repeats | PCR | Rapid, sensitive | Requires optimization | | mtDNA | Mitochondrial genome | Sequencing | Works with minimal DNA | Lower discrimination, maternal inheritance | **Clinical Pearl:** RFLP-VNTR fingerprinting was revolutionary in forensic medicine but has been largely replaced by STR profiling due to speed and ability to work with degraded DNA. However, RFLP remains the historical gold standard and is still asked in NEET PG examinations. **Mnemonic:** **RFLP-VNTR = Restriction Fragment Length Polymorphism using Variable Number Tandem Repeats** [cite:Vij Textbook of Forensic Medicine Ch 9]