As all living things contain DNA, and all DNA exhibits variability both among and within species, any biological material associated with a legal case carries in it information about its source (Mark A. Jobling e'tal).The major advantage of DNA based technique is requirement of very small amount of sample like drop of body fluid, cigarette butts , or hair is enough to determined the identity of criminal or person related to crime.
There is almost century old history of forensic genetics started with human ABO blood group polymorphisms. It was used for quite long time but having few drawbacks it was not used quite frequently in present investigations. The major back trough occurred in 1984 when Alec Jeffreys identified the hyper variable loci known as MINISATELLITE. The banding pattern obtained from this micro satellite known as DNA fingerprinting and was widely used since it discovery. The only drawback of this system is complicated data and difficulty to interpret. Than
Development of 'single-locus probes' (SLPs) here it revealed only a single, highly polymorphic, restriction fragment length polymorphism. And hence simplifying interpretation. In Typical SLP based investigation four SLPs were used successively to probe a Southern blot, yielding eight hyper variable fragments per individual.( Mark A. Jobling e'tal). ...
Being sensitive, high discriminating power and reliable in case of mix sample qualifies STR as perfect forensic tool.
Fig 1 shows chronologic evolution of forensic genetics (Nat Rev Genet. 2004 Oct; 5 (10):739-51.)
STR (Short tandem repeat):
STR, short tandem repeat are short sequences of DNA normally of length 2-5 base pairs. and one can fine numerous time repetition of these sequences. There are almost 10,000 published STR sequence available in different literature. most widely used STRs are tetra or penta tendon repeat as there are certain advantage of smaller repeat over larger one, like it can withstand DNA degradation and avoids preferential amplification during PCR. Similarly short repeat is getting attention in terms of genetic diseases like tri-nucleotide repeat associated Huntington disease. STR markers are mainly classified under two category 1) Autosomal STR and 2) Y-chromosomal STR.
1) Autosomal STR:
Initially there were four simple STR were used but there were high probability of similar matching hence later on it raise two more Complex STR along with PCR assay targeted at the XY-homologous amelogenin genes. As Forensic experts realized the capability of STR based identification system more attention was provided toward development of standard technique. In this line four more loci were added in to the over all process and name as SGM plus. Based on this development effort were made to set up STR database to mention record of individual having crime history. There are some differences between the overall techniques employed for STR typing in different countries and legal systems. For example in USA FDI CODI Shaving 16