DNA Fingerprinting

The technique of identifying an individual by analyzing the unique DNA sequence present in each person, similar to fingerprints, is called DNA fingerprinting.

Why is DNA Fingerprinting Possible?

• Every person has a unique DNA pattern except identical twins.​
• Many DNA regions are highly conserved, but some regions show variation among individuals.​
• These variable regions can be studied and compared to establish identity or a biological relationship.​

Important Basis

• DNA fingerprinting mainly uses satellite DNA, especially VNTRs (Variable Number Tandem Repeats).​
• VNTRs are short nucleotide sequences repeated many times in tandem.​
• The number of repeats varies from person to person, producing DNA polymorphism.

DNA fingerprinting works on the principle that some non-coding DNA regions show high variability among individuals.​ When such regions are isolated and analysed, they produce a characteristic banding pattern that can be compared between samples.​

1. DNA from different individuals contains repetitive regions such as VNTRs.​
2. The number of repeats in these regions differs among individuals.​
3. These differences produce DNA fragments of different lengths.​
4. After separation and detection, the fragments appear as distinct bands.​
5. Matching band patterns suggest identity or close biological relation.

1. Isolation of DNA
   DNA is extracted from the sample, such as blood, hair root, skin tissue, semen, or other biological material.​
2. Amplification of DNA
   If the sample amount is very small, the DNA is amplified using PCR.​
3. Digestion with Restriction Enzymes
   DNA is cut into fragments using specific restriction endonucleases.​
4. Gel Electrophoresis
   DNA fragments are separated according to size by passing them through a gel matrix under an electric field.​
5. Southern Blotting
   The separated DNA fragments are transferred from the gel onto a membrane.​
6. Hybridisation with Probe
   A labelled probe complementary to the VNTR sequence is added to detect the required DNA fragments.​
7. Autoradiography / Detection
   The hybridised fragments appear as bands, forming the DNA fingerprint.​

DNA Fingerprinting

Schematic representation of DNA fingerprinting: Few representative chromosomes have been shown to contain different copy number of VNTR

Major Uses:

• Forensic science: identification of criminals using biological samples.​
• Paternity and maternity disputes: establishing biological relationships.​
• Pedigree and family studies: tracing inheritance patterns.​
• Medical diagnosis and research: studying inherited disorders and genetic variation.​
• Conservation biology: identifying endangered species and analysing biodiversity.​
• Anthropological and evolutionary studies: understanding genetic relationships among populations.

• DNA fingerprinting is a technique used to identify an individual by analysing the unique DNA pattern present in every person (except identical twins).
• It is based on satellite DNA, especially VNTRs (Variable Number Tandem Repeats) - short sequences repeated in tandem, whose number varies among individuals and creates DNA polymorphism.
• Principle: the differences in VNTR repeat number produce DNA fragments of different lengths, which appear as a unique banding pattern.
• Steps: DNA isolation → PCR amplification → restriction digestion → gel electrophoresis → Southern blotting → probe hybridisation → autoradiography → comparison of band patterns.
• Applications: forensic identification, paternity/maternity testing, pedigree studies, medical research, conservation biology, and evolutionary/anthropological studies.