DNA fingerprinting (DNA profiling)
Definition
DNA fingerprinting is a molecular technique used to identify an individual based on unique patterns in their DNA.
It analyzes highly variable repetitive DNA sequences, mainly VNTRs (Variable Number Tandem Repeats) and STRs (Short Tandem Repeats).
Except for identical twins, every individual has a unique DNA profile.
Principle
Human DNA contains regions that vary greatly among individuals.
The number of repeat units at specific loci differs from person to person.
These variations produce DNA fragments of different lengths, generating a characteristic banding pattern.
The DNA profile is inherited from parents and remains largely unchanged throughout life.
Basis of DNA fingerprinting
VNTRs: tandem repeats of 10–100 base pairs.
STRs: tandem repeats of 2–6 base pairs.
STR analysis is preferred in modern forensic laboratories because it requires less DNA and provides higher accuracy.
Steps involved in DNA fingerprinting
Collection of biological sample (blood, saliva, semen, hair root, tissue, etc.).
Isolation of DNA from the sample.
Amplification of target DNA using Polymerase Chain Reaction (PCR).
Separation of DNA fragments by gel electrophoresis or capillary electrophoresis.
Detection of DNA fragments using fluorescent labeling or DNA probes.
Comparison of DNA profiles between samples.
The fragment separation step is commonly visualized by electrophoresis.
Role of Alec Jeffreys
Sir Alec Jeffreys developed DNA fingerprinting in 1984 at the University of Leicester, UK.
He discovered that minisatellite DNA sequences show extensive variation among individuals.
Applications
Forensic science: identification of criminals from biological evidence.
Paternity and maternity testing: determination of biological relationships.
Identification of missing persons.
Disaster victim identification.
Wildlife conservation: identification of endangered species and prevention of illegal trade.
Population genetics and evolutionary studies.
Medical genetics: linkage analysis and inheritance studies.
Advantages
Highly specific and reliable.
Requires only a small amount of DNA.
Can analyze old or partially degraded samples (especially STR-based methods).
Useful in both criminal investigations and civil disputes.
Limitations
DNA contamination can affect results.
Closely related individuals share many DNA markers.
Identical twins have nearly identical DNA profiles.
Proper sample collection and laboratory quality control are essential.
Modern DNA fingerprinting
Modern profiling uses PCR amplification of multiple STR loci and computerized comparison of allele patterns. This method has largely replaced the older RFLP (Restriction Fragment Length Polymorphism) technique.
Difference between RFLP and STR profiling
RFLP | STR profiling |
|---|---|
Requires large amount of DNA | Requires very little DNA |
Works best with intact DNA | Works with degraded DNA |
Slow and labor-intensive | Rapid and automated |
Uses restriction enzymes | Uses PCR amplification |
Important exam points
DNA fingerprinting is based on DNA polymorphism.
The most commonly used markers are STRs.
PCR is an essential step in modern DNA profiling.
DNA fragments are separated by electrophoresis.
The probability of two unrelated individuals having the same STR profile is extremely low.
References
NCERT. (2025). Biology, Class XII. Chapter: Biotechnology and Its Applications. National Council of Educational Research and Training, New Delhi.
Alberts, B., et al. (2022). Molecular Biology of the Cell (7th ed.). Garland Science.
Watson, J. D., et al. (2014). Molecular Biology of the Gene (7th ed.). Pearson.
Butler, J. M. (2015). Advanced Topics in Forensic DNA Typing: Interpretation. Academic Press.
Jeffreys, A. J., Wilson, V., & Thein, S. L. (1985). Hypervariable “minisatellite” regions in human DNA. Nature, 314(6006), 67–73.
Brown, T. A. (2018). Genomes 4. Garland Science.