Question

Briefly describe the technique employed in DNA fingerprinting.

Answer 1

The technique employed in DNA fingerprinting.

• Extraction of DNA from the sample cells.
• Amplification : Making many copies of DNA is called amplification. It is done by a technique called polymerase chain reaction (PCR).
• Restriction digestion : DNA is then cut into sections by using restriction endonucleases.
• Separation of DNA sequences : In this process, DNA fragments are separated by using gel electrophoresis.
• Southern blotting (named after its inventor E. M. Southern). In this process, separated DNA sequences are transferred from gel onto a nylon membrane.
• Hybridisation using labelled VNTR probe : In this process, radiactive DNA probes are attached to specific portions of the DNA fragments. Thereafter any DNA not attached to the probes is washed off.
• Detection of hybridised DNA fragments by autoradiography : The remaining DNA is then exposed to X-ray film. The radioactive probes on the DNA are allowed to expose the film, which, when developed reveals a unique pattern of dark and light bands. These bands give a characteristic pattern for an individual DNA. It differs from individual to individual in a population except in the case of monozygotic (identical) twins. The sensitivity of the  technique can be increased by use of polymerase chain reaction. Consequently, DNA from a single cell is enough to perform DNA fingerprinting analysis. Currently many different probes are used to generate DNA fingerprints.