DNA Fingerprinting

Biometrics relies on distinctive individual physiological traits. Within such traits, DNA (Deoxyribo Nucleic Acid)–the hereditary material that determines what genetic traits we inherit–is supposed to be the most distinctive. Structurally, it is a long double-helical chain of a phosphate backbone, to which are attached ribose sugars and nitrogenous bases. It is like a code that directs our body cells to make or assemble things that are required for the functioning of our body. Though, within such a large molecule, a first glance will not show up a significant difference in the ‘code’, even a single insignificant change in the sequence leads to the differences that we see. So much so for biology. Let us look at how this is utilized in identifying individuals.

A DNA molecule is divided into small functional units called genes, which determine your black hair and brown eyes. DNA samples can be taken from the body if the subject or his personal belongings are passed through chemical processes. This DNA fingerprint is in the form of a sequence of A’s, T’s, G’s and C’s in random order. These alphabets refer to the nitrogenous bases.

Sounds easy? Now comes the difficult part. The length of this sequence is immense and beyond comprehension! Here is where matching algorithms come into picture. There are lots of schemes that are followed for generating these algorithms. The most widely used is a kind of an indexed algorithm, which is also probabilistic in nature. What this means is that these algorithms look for matches only in those places where they are most likely to find a match and ignore the rest of the database. From an existing database, the algorithm generates indices and then matches the sequence under consideration, with them.

The next step in DNA sequence matching is matching the shape of molecules. Biologists say that much of what function a protein will do is also dependent on the shape it takes. But researchers face another problem here. A protein molecule here can be in a variety of similar but not same orientations. Hence researchers need to look at ‘rigid elements’ of molecules and the way the non-rigid elements are connected to them. Molecules with similar rigid elements would then form a group. Algorithms then analyze and match DNA sequences accordingly.

DNA matching has advantages over other means of biometric verification. DNA samples can be collected in many more forms than blood samples, retina scans or fingerprints. Even the personal belongings of people like hairbrushes, toothbrushes or clothes carry their DNA from phenomenon like natural skin flaking. So it becomes close to impossible for an imposter to fake a DNA sample or avoid leaving a trace at a crime scene. The only drawback is that DNA testing takes longer than other methods, something like a couple of days to a week. But constant research will soon have faster, if not real-time, DNA analyzers that will ensure punishment for the guilty and justice to the innocent.

Ashish Sharma