Forensic Dna Profiling

Forensic science, being the application of science to law, has applied many scientific techniques used in other fields of the analytical sciences to address questions raised in a legal context. The application of DNA technology, and in particular the use of the polymerase chain reaction (PCR), has revolutionized the field of human identification. The first use of DNA in forensic science was to help solve a sexual assault in England. Professor Sir Alec Jeffreys coined the term ''DNA fingerprinting''[1] when he was able to link two sexual assaults as committed by the same perpetrator and then to link the crime scene sample to the suspect, Colin Pitchfork. Previous examination of biological evidence used genetic polymorphisms producing different proteins; however, as the human genome is approximately 3 billion base pairs in size and that less than 3% is gene related, greater polymorphism lay in the non-gene-related regions. It was always considered that the DNA from each individual was unique, with the exception of monozygotic twins. Professor Sir Alec Jeffreys noted that there were regions of DNA where the same sequence of DNA was repeated many times. The number by which this repeat motif was found along the chromosome of different people was found to differ. These regions, termed variable number tandem repeats (minisatellites), were exploited in DNA fingerprinting. The field of DNA profiling has now moved to the analysis of hypervariable short tandem repeats (STRs). Short tandem repeats are short regions of DNA, typically 2-8 DNA bases in length, that are repeated polymorphically along the chromosome. The first use of STRs was in 1994 when four separate DNA loci were amplified in one reaction.[2] Within 1 year the multiplex PCR had increased to six independent STR DNA loci.[3] Short tandem repeats are regions of DNA found close to genes, often within introns, in which a sequence of DNA is repeated. The repeat motif is frequently 4 bp in length with the number of repeats varying from 6 to over 30. The number of repeats is known to be highly variable, producing size variations at the loci. The flanking DNA on either side of the STR loci is known to be highly conserved allowing amplification of the locus by PCR using primers made to the flanking DNA. Primers have been designed that will work on all the major ethnic populations.

With increased knowledge of the PCR process the number of loci that could be successfully and routinely amplified increased to a point where currently 10 STR loci form the basis for the National DNA Database (NDNAD) in the United Kingdom. In the United States 13 loci form the Combined DNA Index System, or CODIS. Short tandem repeats are highly abundant in the human genome and are known to be polymorphic.[4,5]

While one STR locus provides little power of discrimination, it is common to analyze 10 STR loci in a single multiplex reaction. Each of the loci examined is independently inherited producing an overall power of discrimination of greater than a billion. This equates to close to identity and meets the current needs of the forensic community.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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