DNA Fingerprinting
டிஎன்ஏ கைரேகை
99.9% of human DNA is identical across all individuals. The remaining 0.1% is where your identity, your crimes, and your paternity are locked. If you confuse VNTRs with SNPs, you lose 4 marks. Focus.
The idea
DNA fingerprinting relies on identifying polymorphisms in repetitive DNA sequences known as Variable Number of Tandem Repeats (VNTRs). The process involves isolating DNA, digesting it with restriction endonucleases, and separating fragments via gel electrophoresis. These fragments are transferred to synthetic membranes through Southern blotting and hybridized using radioactive VNTR probes. Finally, the pattern is detected by autoradiography to create a unique genetic profile.
Why it matters
It exists because while 99.9% of human DNA is identical, the highly polymorphic repetitive regions provide a unique genetic signature for every individual.
NEET lens
NEET focuses on the sequence of steps: Isolation, Digestion, Electrophoresis, Blotting, Hybridization, and Autoradiography. Memorize that VNTRs are satellite DNA. Do not confuse 'probes' with 'primers'. Expect questions on the specific role of Southern blotting in this process.
Clinical significance
DNA fingerprinting is the gold standard for forensic investigations and paternity testing. Failure in this technique leads to miscarriages of justice or incorrect medical diagnoses in cases of disputed parentage. It is also critical in identifying genetic markers for hereditary diseases within a population.
Introduction
DNA fingerprinting is a quick way to compare DNA sequences of two individuals by looking at repetitive DNA, which differs from person to person.
Core concept
Basis: satellite DNA — repeated sequences (VNTRs, variable number of tandem repeats) that show high polymorphism. Technique (Alec Jeffreys): isolation of DNA → digestion with restriction endonucleases → separation of fragments by gel electrophoresis → transfer (blotting) to nitrocellulose or nylon membranes → hybridisation using labelled VNTR probe → detection by autoradiography. The VNTR probe was used by Jeffreys. Uses: forensic science, paternity testing, determining population and genetic diversity. Polymerase chain reaction can increase sensitivity, but the classic technique does not need it.
Go deeper
DNA polymorphism (variation at the DNA level, an allele frequency above 0.01 in a population) is the basis of genetic mapping and DNA fingerprinting. Satellite DNA does not code for proteins but forms a large portion of the genome.
From Class 10
Just as fingerprints on your hand are unique, the pattern of repeated DNA pieces is unique to each person (except identical twins).