HYDERABAD: Scientists at the Hyderabad-based Centre for DNA Fingerprinting and Diagnostics (CDFD) have given a way forward to human identification through DNA sample in case of the sample being heavily degraded like in cases of exhumed bones or burnt bodies.
This has been made possible as the scientists, headed by Dr N Madhusudan Reddy, head of laboratory of DNA Fingerprinting Services, CDFD, have established 70 positions of Single Nucleotide Polymorphism (SNP) that can be used as markers for human identification in Indian population.
As of now, the technique being used for human identification through DNA samples in India is known as Short Tandem Repeat (STR) analysis which cannot be used if DNA sample is degraded. DNA is a chain in which nucleotides—adenine, thymine, cytosine and guanine—are arranged in a similar manner as in all humans. In this arrangement either one or more of these nucleotides are arranged in such a sequence which repeats itself consecutively a few times. The number of times this sequence repeats differs from person to person across the world.
In STR analysis, a collected DNA sample is analysed for this frequency and is matched with the available sample.
For this the DNA sample should be a long strand of approximately 500 base pairs. In SNP analysis, a small DNA strand is enough to identify a sample, less than 100 base pairs. As rather than finding repetitive sequence of nucleotides, the nucleotides themselves are individually observed. At some particular positions in DNA there are aberrations in nucleotides and these aberrations vary from one person to another across the world. The CDFD study found 205 such positions, of which 70 positions gave a billion-fold increase in DNA matching probability as compared to the 48 European positions.
Next Step
Dr Reddy says that the next step would be to use the SNP technique as devised by him for analysing DNA samples and identifying humans in real life cases which would further establish the credibility of the new technique.
After this, hybrid kits can be developed, which can be used to analyse collected DNA samples using STR and SNP techniques like it is currently being done in some countries.