DNA profiling and its scientific value in establishing guilt or innocence in the justice system

Sub: Sci

Sec: Health

The accuracy of DNA evidence is increasing with the advancement of science with every passing day, thereby making it more and more reliable, but yet we have not reached a juncture where it may be called infallible.

What is DNA profiling?

DNA profiling is the process where a specific DNA pattern, called a profile, is obtained from a person or sample of bodily tissue.
Human DNA profiles can be used to identify the origin of a DNA sample at a crime scene or test for parentage.
Each individual inherits a unique combination of polymorphisms from their parents and these DNA polymorphisms are analyzed to give a DNA profile.
DNA profiling includes isolation, purification and quantitation of DNA, amplification of selected genetic markers, visualizing the fragments and genotyping, statistical analysis and interpretation, the Kolkata lab explainer adds.

What is the source of DNA profiling?

DNA can be sourced from any biological material.
This includes saliva, semen, vaginal fluids, blood, body tissues, teeth, hair, and bones.
The quantity of DNA contained in biological material varies as blood and saliva are richer sources of DNA as compared to teeth and hair roots, which are DNA deficien
Touch DNA contains very low amounts of DNA and is not an ideal source for DNA profiling.

How reliable is DNA?

DNA in all human beings is 99.9% identical.
In forensic DNA profiling, a few locations in the remaining 0.1% of DNA are chosen to create a person’s DNA profile.
These specific locations at which the DNA is examined are called loci which have repetitive sequences of DNA called Short Tandem Repeats, or STRs.
While every individual has the same sequence, or STR, on a locus, the number of times that it repeats itself may vary across individuals.
The current genetic markers of choice for forensic purposes are STRs.
STRs present on the Y chromosome are used in sexual assault cases or to determine paternal lineage.

How conclusive is DNA profiling?

Manikanda Raj, head of forensic medicine and toxicology at Chengalpattu Medical College and Hospital, says DNA analysis as a process is based on probability and, in that sense, cannot be considered conclusive evidence.
As per the The Madras High Court verdict there are three possible outcomes of a profile comparison-
- (1) Match : If the DNA profiles obtained from the two samples are indistinguishable, they are said to have matched.
- (2) Exclusion : If the comparison of profiles shows differences, it can only be explained by the two samples originating from different sources.
- (3) Inconclusive : The data does not support a conclusion.
As per the Law Commission of India report If the samples match, that does not mean the identity is conclusively proved.
Thus, DNA may be more useful for purposes of investigation but not for raising any presumption of identity in a court of law.