In August 1999,a young student of University of Virginia student was sexually assaulted and raped after pointing a gun at her by the assailant. The things inside the house were stolen. The girl was asked to have a shower by the assailant so that any trace of evidence can be removed. He left sample of saliva in the beer can and semen sample in the bed. After six long weeks in October 1999 a match was obtained from the Virginia Dna Database.
The criminal justice system is divided into three broad categories:-
- Law Enforcement
- Scientific Analysis
- Legal proceedings
Investigators and detectives submit evidence to the forensic Laboratories. Scientist compares the crime scene sample to the reference samples or compared against DNA Database. The scientific report was submitted to the court for legal proceedings to make any further decisions.
DNA profiling was first described by Alec Jeffreys, an English Geneticist. DNA sequences were repeated and are called Variable Number Tandem Repeats (VNTR).Jeffrey did Restriction Fragment Length Polymorphism to cut the regions of DNA around VNTR. The RFLP method was used to solve and identify the rapist and murderer Colin Pitchfork.
STEPS IN DNA sample processing
DNA from the biological material was extracted. DNA is amplified using polymerase Chain Reaction using STR markers and quantified. Very small of amount of DNA is required to multiplex the PCR reactions. Multiple STR regions can be examined to increase the amount of information from the biological evidence. The PCR products (amplicons) are separated according to the size in using Capillary Electrophoresis in a genetic analyzer .DNA obtained rom the question sample and reference samples were compared. The results can be exclusion, inclusion or inconclusive. The end result of a forensic examination is a Laboratory Report.
History of DNA Typing
- In 1985 Alec Jeffreys develops multi locus RFLP probes.
- In 1991 fluorescent STR markers were first described.
- In 1993,amelogenin locus was developed and first STR kit was developed.
- In 1997 13 STR loci and Y chromosome loci was established.
- In2002,FBI mtDNA population database was released.
- In 2003,US DNA database, National DNA Index System (NDIS) exceeded 1 million convicted offender profiles.
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