Definition
DNA fingerprinting (DNA profiling) is a
molecular technique used to identify individuals based on unique patterns in
their DNA. It analyzes highly variable regions called VNTRs (Variable Number
Tandem Repeats) or STRs (Short Tandem Repeats). Developed by Sir Alec Jeffreys
in 1984.
Principle
·
More than 99.9% of human DNA is
identical, but repetitive DNA regions vary among individuals.
·
The number of repeat units
differs from person to person.
·
These variations produce a unique
DNA banding pattern for each individual (except identical twins).
Types of DNA Sequences Used
|
Sequence type |
Characteristics |
|
VNTRs |
Long tandem repeats (10–100 bp) |
|
STRs |
Short tandem repeats (2–6 bp) |
Modern
forensic analysis mainly uses STR markers.
Steps of DNA Fingerprinting
1.
Sample collection
DNA can be obtained from blood, hair root,
saliva, semen, bone, teeth, and skin cells.
2.
DNA isolation
DNA is extracted from the collected
biological sample.
3.
DNA amplification (PCR)
Specific STR/VNTR regions are amplified
using the Polymerase Chain Reaction (PCR).
4.
Restriction digestion (classical method)
Restriction enzymes cut DNA into fragments
at specific sequences.
5.
Gel electrophoresis
DNA fragments are separated according to
size through an agarose gel.
6.
Southern blotting
DNA fragments are transferred from the gel
onto a nylon or nitrocellulose membrane.
7.
Hybridization with labeled probes
Radioactive or fluorescent probes bind to
specific repetitive DNA sequences.
8.
Detection
Band patterns are visualized using
autoradiography or fluorescence detection. The resulting pattern is the DNA
fingerprint.
Workflow
Biological sample → DNA extraction → PCR
amplification of STR/VNTR loci → Gel electrophoresis → Southern blotting →
Probe hybridization → DNA fingerprint pattern
Applications
Forensic
science: Identification of criminals, matching
biological samples, and crime scene investigation.
Paternity
and maternity testing: Establishing biological
relationships and resolving inheritance disputes.
Identification
of missing persons: Disaster victim identification
and unknown body identification.
Medical
genetics: Detection of inherited disorders and
linkage analysis.
Wildlife
conservation: Identification of endangered species
and prevention of illegal wildlife trade.
Evolutionary
and population studies: Genetic diversity analysis
and human migration studies.
Advantages
·
Highly accurate
·
Requires a very small DNA
sample
·
Useful even with degraded DNA
·
Fast analysis using PCR
·
High discriminatory power
Limitations
·
Identical twins have the same
DNA fingerprint.
·
Contaminated samples may give
misleading results.
·
Improper handling can affect
accuracy.
·
Interpretation requires
statistical analysis.
DNA Fingerprinting in India
The technique was developed in India by Dr.
Lalji Singh, known as the Father of DNA Fingerprinting in India. He introduced
DNA fingerprinting technology for forensic and paternity investigations in the
country.
Important NEET Points
·
Inventor: Alec Jeffreys (1984)
·
Indian pioneer: Dr. Lalji Singh
·
Main markers used today: STRs
·
Technique involved: PCR + Gel
electrophoresis
·
Classical method: Southern
blotting
·
Used in: Forensics, paternity
testing, and identification
Academic References
1.
Jeffreys, A. J., Wilson, V.,
& Thein, S. L. (1985). Hypervariable "minisatellite" regions in
human DNA. Nature, 314, 67–73.
2.
Alberts, B., et al. (2022).
Molecular Biology of the Cell (7th ed.). Garland Science.
3.
NCERT. (2025). Biology, Class
XII. Chapter: Biotechnology and its Applications.
4.
Butler, J. M. (2015). Advanced
Topics in Forensic DNA Typing: Interpretation. Academic Press.
5.
Jobling, M. A., & Gill, P.
(2004). Encoded evidence: DNA in forensic analysis. Nature Reviews Genetics, 5,
739–751.
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