DNA FINGERPRINTING (DF)
DNA FINGERPRINTING (DF)
- The chemical structure of everyone’s DNA is the same. The only difference between people or any animal is the order of the base pairs.
- There are so many millions of base pairs in each person’s DNA that every person has a different sequence except identical twins.
- Using these sequences, every person could be identified solely by the sequence of their base pairs. However, because there are so many millions of base pairs, the task would be very time-consuming.
- Instead, scientists are able to use a shorter method, because of repeating patterns in DNA. These patterns do not, however, give an individual “fingerprint,” but they are able to determine whether two DNA samples are from the same person, related people, or non-related people.
- DNA Fingerprinting (also called DNA typing, DNA testing or DNA profiling) is the technology of identifying individuals from certain repeating sequences in their DNA, that don’t code for any protein, which are termed as VNTRs (Variable number Tandem repeats) or Minisatellites.
- For example, ATTCG ATTCG ATTCG, in which sequence ATTCG is repeated thrice. The technology was developed by British geneticist ‘Alec Jeffreys’ (1984) at the University of Leicester in England.
TECHNIQUES | DNA FINGERPRINTING (DF)
- DNA sample typically called a ‘reference sample’ is obtained which can either be in the form of skin, blood, hair saliva, tear etc.
- From these samples, DNA is first isolated, extracted & purified.
- Cut in to segments of various lengths using restriction enzymes.
- DNA fragments of various lengths are sorted according to size by a technique known as gel electrophoresis.
- At the end, sorted double stranded DNA fragments are subjected to heat or chemically treated to break them up in to the single strands.The band pattern of Single Stranded DNA obtained is then blotted (transmitted) to a nylon or nitrocellulose membrane. This is known as Southern Blotting.
- When the southern blot is treated with a single strand DNA ‘Probe’ tagged with a radioactive isotope, a unique DNA pattern with part of it containing radioactive isotope is left behind.
- If a sheet of X-ray film is now placed in contact with the southern blot, only the areas where radioactive probe binds show up on the film. The resulting pattern of dark bands on the developed X-ray film is the DNA fingerprint.
USES | DNA FINGERPRINTING (DF)
- DNA Fingerprinting can be used to identify & convict criminals in cases of murder and rape.
- It serves as a powerful tool for settling paternity disputes & identifying dead persons.
- It is also used for the purpose of detecting genetic disorder, pedigree analysis & in identifying genetic stock.
In India, pioneering work in developing DNA probes for DNA fingerprinting has been done by ‘LaIji Singh’ at Centre for Cell and Molecular Biology (CCMB), Hyderabad. Other centres exclusively for DNA fingerprinting are Centre for DNA Fingerprinting & Diagnostics (CDFD), Hyderabad and Central Forensic Science Laboratory (CFSL), Kolkata.