DNA Fingerprinting
DNA fingerprinting is a technique for identifying repeated sequences in the human genome that produce a pattern of bands unique for every individual.
- Dr Alec Jeffreys, a geneticist from the University discovered DNA fingerprinting in September 1984.
- Lalji Singh FNA, FASc (5 July 1947 – 10 December 2017) was an Indian scientist who worked in the field of DNA fingerprinting technology in India, where he was popularly known as the “Father of Indian DNA fingerprinting“.
Satellite DNA is part of repetitive DNA with long repetitive sequences in tandem that form a separate fraction on density gradient centrifugation. Satellite DNA shows a very high degree of polymorphism. It is called the variable number of tandem repeats (VNTR). Polymorphism (variation at the genetic level) arises due to mutations.
In DNA polymorphism, more than one variant (allele) at a locus occurs in the human population with a frequency greater than 0.01. DNA fingerprints can be prepared from extremely minute amounts of blood, semen, hair bulb or any other cells of the body.
Major Steps of DNA Fingerprinting:
- DNA is extracted from the cells. DNA can be amplified by PCR or polymerase chain reaction.
- DNA is cut into fragments with restriction enzymes.
- Chopped DNA fragments are passed through electrophoresis. The separated fragments can be visualized by staining them with a dye.
- Double-stranded DNA is then split into single-stranded DNA using alkaline chemicals.
- Separated DNA sequences are transferred from the gel onto a nitrocellulose or nylon membrane, this process is called the southern blotting technique.
Southern Blotting Technique
- The nylon sheet is then immersed in a bath, where probes or markers (radioactive synthetic DNA segments of known sequences) are added. The probe hybridizes with VNTR.
- X-ray film is exposed to the nylon sheet gives dark bands at the probe sites. Thus, hybridized fragments are detected by autoradiography.
DNA fingerprinting helps in identifying the true (biological) father, criminal and it can solve the problems of evolution.
