Method of DNA Fingerprinting
In this technique DNA is isolated from blood stains, semen stains or hair roots of disputed children or any suspected person and the same from parents, close associates or relatives of suspected criminals (based on the cases). Since hairs contain less amount of DNA, it can be produced in a large amount by using polymerase chain reaction (PCR). RBCs do not contain DNA, therefore, WBCs are the source of DNA. Thus the DNA isolated is cut with restriction enzyme and subjected to Southern blotting. The DNA bands appearing on membrane are hybridized with 32P-DNA probe, washed in water to remove unhybridized DNA, and passed through X-ray. The hybridized complementary DNA sequences develop images (prints). Identical prints that contain specific DNA sequences appearing on two X-ray films are identified and thus identity is confirmed. Probability of two persons having similar sets of base pairs in the same sequence of VNTR of DNA is one in 30-300 million individuals.
In India, facilities of DNA fingerprinting at international level are available at the Center for DNA Fingerprinting and Diagnostics (CDFD) (Hyderabad), the then Center for Cellular and Molecular Biology (CCMB) (Hyderabad). At this center the Jeffreys technique is not followed. Dr. Lalji Singh has developed an indigenous technique where 'BKM'-DNA probe is used for hybridization of DNA sequences. While he was working on sex determination in snakes in his Ph.D. programme (in BHU, Varanasi), he found a contrast result. Unlike human and other organisms, the female snake contains XY and the male YY sex chromosomes. A segment of DNA was isolated from sex determining Y chromosome of female banded krait (Bungarus fasciatus), an Indian poisonous snake. This unique segment was named as 'banded krait minor satellite' (BKM). It is similar to sex determining chromosome in humans. The probe which is used for this purpose is, therefore, called BKM-DNA probe.