Invention of polymerase chain reaction and thermo stable DNA polymerase has revolutionized this concept. Many techniques like Variable tandem repeat (VNTRs) and Short Tandem Repeat(STRs) based Amplified Fragment Length Polymorphism(AFLP) or DNA fingerprinting, Gender ID (Amelogenin), Mitochondrial D-Loop DNA for Maternal identification etc. have been developed for forensic investigations. PM&DQA1 is the first PCR based typing system, developed by the scientist at Cetus Corporation and commercialized by Applied Biosystems. Inc. PM& DQA1 is simple and rapid technique mainly employed in case of limited DNA sample or in case of highly degraded DNA. The test is performed on 6 different loci to investigate pleomorphism using hybridization based Reverse DOT-BLOT methodology. The major limitation of this technique is its differentiating power due to limited diversity found among 6 loci among different human population.
Crime investigation obtained new direction after invention of DNA based techniques for identification of criminals. The biggest advantage of DNA based techniques is the requirement of very small amount of biological samples which includes blood, hair, semen etc. Invention of polymerase chain reaction (PCR) and thermo stable DNA polymerase has revolutionized these DNA based techniques due to its immense power of DNA multiplication. There are many DNA based techniques that are employed for detection of crime and criminals including Restriction Fragment Length Polymorphism (RFLP), Variable tandem repeat (VNTRs) and Short Tandem Repeat(STRs) based Amplified Fragment Length Polymorphism(AFLP) or DNA fingerprinting, Gender ID (Amelogenin), Mitochondrial D-Loop DNA for Matrilineal identification. Criminal identification based on human body parts or component has been used since last century as part of forensic investigations. The classical example being Human finger prints which was recognized by British physician Sir Francis Galton (1). In the beginning of 20th century many physiologists and doctors realized that blood cell has distinct antigens and they are different from individual to individuals. Initially blood cell antigens were taken into consideration only in case of blood transfusion and surgery but later on its forensic utilities were realized and it was employed to solve problem of paternity dispute, child mix-up etc. Those days blood samples saliva and semen samples were produced in court as evidence against criminals but it was not taken as conclusive evidence due to its limited distinguished power. In 1970, the things started to change after discovery of DNA structure and the increases in the understanding of its variability between individual to individual. Once DNA was established as target molecule for forensic investigation, many researchers came forward with different methodology and different locus having higher variability like micro and mini satellites. Initially there were many questions that were raised over methodologies and interpretation of DNA based identification systems. But thorough investigation and population genetics based