🔍 DNA Fingerprinting
Learn DNA fingerprinting using VNTR and STR markers for CUET Agriculture. Southern blotting, RFLP, PCR methods and forensic applications.
Introduction
- Developed by Sir Alec Jeffreys (1984) at the University of Leicester, UK.
- Also called DNA profiling or DNA typing.
- Based on the fact that every individual (except identical twins) has a unique pattern of repetitive DNA sequences — just as no two people have the same fingerprints.
Basis: Repetitive DNA (VNTRs)
The human genome contains large amounts of repetitive DNA:
| Type | Repeat Unit | Description | Use |
|---|---|---|---|
| Satellite DNA | Variable | Highly repetitive; found at centromeres | Chromosome structure |
| Minisatellite / VNTR | 10-60 bp | Variable Number of Tandem Repeats; copy number varies between individuals | Used in original DNA fingerprinting (Jeffreys) |
| Microsatellite / STR (SSR) | 1-6 bp | Short Tandem Repeats; PCR-compatible | Modern forensic profiling (replaced VNTRs) |
NOTE
The number of tandem repeats at each VNTR locus varies between individuals → produces a unique banding pattern. A child inherits half their VNTR alleles from each parent, so the child's fingerprint is a composite of both parents' patterns.
🔐
Pro Content Locked
Upgrade to Pro to access this lesson and all other premium content.
Pro
Popular Save ₹100/mo
₹ 99 /mo
₹99 charged monthly · Cancel anytime
- All Agriculture & Banking Courses
- AI Lesson Questions (100/day)
- AI Doubt Solver (50/day)
- Glows & Grows Feedback (30/day)
- AI Section Quiz (20/day)
- 22-Language Translation (100/day)
- Recall Questions (20/day)
- AI Quiz (15/day)
- AI Quiz Paper Analysis (100/day)
- AI Step-by-Step Explanations (100/day)
- Spaced Repetition Recall (FSRS)
- AI Tutor
- Immersive Text Questions
- Audio Lessons — Hindi & English
- Mock Tests & Previous Year Papers
- Summary & Mind Maps
- XP, Levels, Leaderboard & Badges
- Generate New Classrooms
- Voice AI Teacher (AgriDots Live)
- AI Revision Assistant
- Knowledge Gap Analysis
- Interactive Revision (LangGraph)
🔒 Secure via Razorpay · Cancel anytime · No hidden fees
Introduction
- Developed by Sir Alec Jeffreys (1984) at the University of Leicester, UK.
- Also called DNA profiling or DNA typing.
- Based on the fact that every individual (except identical twins) has a unique pattern of repetitive DNA sequences — just as no two people have the same fingerprints.
Basis: Repetitive DNA (VNTRs)
The human genome contains large amounts of repetitive DNA:
| Type | Repeat Unit | Description | Use |
|---|---|---|---|
| Satellite DNA | Variable | Highly repetitive; found at centromeres | Chromosome structure |
| Minisatellite / VNTR | 10-60 bp | Variable Number of Tandem Repeats; copy number varies between individuals | Used in original DNA fingerprinting (Jeffreys) |
| Microsatellite / STR (SSR) | 1-6 bp | Short Tandem Repeats; PCR-compatible | Modern forensic profiling (replaced VNTRs) |
NOTE
The number of tandem repeats at each VNTR locus varies between individuals → produces a unique banding pattern. A child inherits half their VNTR alleles from each parent, so the child's fingerprint is a composite of both parents' patterns.
Steps of DNA Fingerprinting (RFLP Method)
Step 1: DNA Extraction
- DNA isolated from biological samples — blood, hair, saliva, semen, tissue.
- Cells lysed; proteins removed by protease; DNA purified.
Step 2: Restriction Enzyme Digestion
- DNA cut with specific restriction endonucleases (commonly Hae III in the original Jeffreys method).
- Produces fragments of different sizes because VNTR regions vary in repeat number → different fragment lengths = RFLP (Restriction Fragment Length Polymorphism).
Step 3: Gel Electrophoresis
- DNA fragments separated by size on an agarose gel using electric current.
- Smaller fragments migrate faster toward the positive electrode (anode — DNA is negatively charged due to phosphate groups).
- Produces a pattern of bands based on fragment size.
Step 4: Southern Blotting
- Technique developed by Edward Southern (1975).
- DNA fragments transferred (blotted) from the agarose gel to a nitrocellulose membrane (or nylon membrane).
- DNA on the membrane is denatured to single strands.
- Preserves the spatial pattern of separated fragments for hybridization.
Step 5: Hybridization with Probe
- A radioactive probe (complementary to VNTR sequence, labeled with ³²P) is added.
- Probe hybridizes with complementary VNTR fragments on the membrane.
- Unbound probe is washed away.
Step 6: Autoradiography
- Membrane exposed to X-ray film.
- Radioactive probe positions appear as dark bands on film.
- The resulting banding pattern is the DNA fingerprint.
Applications of DNA Fingerprinting
- Paternity/Maternity disputes — child's fingerprint is composite of both parents' patterns.
- Criminal identification (Forensics) — matching suspect's DNA with crime scene evidence (blood, hair, semen).
- Identification of disaster/accident victims.
- Immigration disputes — proving family relationships.
- Evolutionary studies — comparing DNA of different species.
- Diagnosis of genetic disorders.
- Pedigree analysis in animal and plant breeding.
- Personal identification (more reliable than traditional fingerprints).
DNA Fingerprinting in India
- Centre for DNA Fingerprinting and Diagnostics (CDFD) — established in Hyderabad, India.
- First case used in Indian courts: 1989.
- CDFD provides DNA fingerprinting services for forensic cases, paternity disputes, and wildlife forensics.
Key Points to Remember
| Fact | Detail |
|---|---|
| Inventor | Sir Alec Jeffreys (1984), University of Leicester |
| Basis | VNTR (Variable Number of Tandem Repeats) — 10-60 bp |
| Restriction enzyme | Hae III (original method) |
| Southern blotting | Edward Southern (1975) |
| Probe label | ³²P (radioactive phosphorus) |
| RFLP | Restriction Fragment Length Polymorphism |
| Modern method | STR/microsatellites (PCR-based; faster than RFLP) |
| India center | CDFD, Hyderabad |
| First Indian court use | 1989 |
| Identical twins | Same DNA fingerprint (cannot be distinguished) |
TIP
The 6 steps in order: Extraction → Digestion → Electrophoresis → Southern blot → Hybridization → Autoradiography. Mnemonic: ED-ESHA.
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| DNA fingerprinting developed by | Sir Alec Jeffreys (1984), University of Leicester, UK |
| Also called | DNA profiling or DNA typing |
| Basis | Every individual (except identical twins) has unique pattern of repetitive DNA |
| Satellite DNA | Highly repetitive; found at centromeres; chromosome structure |
| Minisatellite / VNTR | 10-60 bp repeat units; Variable Number of Tandem Repeats; used in original DNA fingerprinting |
| Microsatellite / STR (SSR) | 1-6 bp repeat units; Short Tandem Repeats; used in modern forensic profiling (PCR-based) |
| Child's fingerprint | Composite of both parents' VNTR patterns (half from each parent) |
| Step 1: DNA Extraction | From blood, hair, saliva, semen, tissue |
| Step 2: Restriction Digestion | Cut with Hae III (original method); produces RFLP fragments |
| Step 3: Gel Electrophoresis | Fragments separated by size on agarose gel; smaller fragments migrate faster toward anode |
| Step 4: Southern Blotting | Developed by Edward Southern (1975); DNA transferred from gel to nitrocellulose membrane |
| Step 5: Hybridization | Radioactive probe (labeled with ³²P) complementary to VNTR sequences |
| Step 6: Autoradiography | Membrane exposed to X-ray film; radioactive bands = DNA fingerprint |
| Mnemonic for 6 steps | ED-ESHA (Extraction, Digestion, Electrophoresis, Southern blot, Hybridization, Autoradiography) |
| RFLP | Restriction Fragment Length Polymorphism — basis of the technique |
| Applications | Paternity disputes, criminal identification (forensics), disaster victim identification, immigration disputes, evolutionary studies, genetic disorder diagnosis, plant/animal breeding |
| CDFD | Centre for DNA Fingerprinting and Diagnostics, Hyderabad, India |
| First Indian court use | 1989 |
| Identical twins | Same DNA fingerprint (cannot be distinguished by this method) |
| Modern method advantage | STR/microsatellites + PCR = faster, needs less DNA than RFLP |
Lesson Doubts
Ask questions, get expert answers