DNA Profiling and the Polymerase Chain Reaction

DNA fingerprinting was developed for individualization system in 1985. Analyses using DNA profiling with variable numbers of tandem repeat polymorphism has been carried out for identification of forensic samples such as bloodstains and sectional stains. Concerning forensic hairs, several DNA analyses of hair root sheath cells have been reported. However, DNA analysis of a hair shaft has not succeed to date, because DNA recovery from a hair shaft is in order of tens of picograms and only low molecular weight DNA (below 200 base pairs (bp)) is left in the hair shape. Recently, microsatellite DNA polymorphism has been detected by the polymerase chain reaction technique. This polymorphism can be applied to DNA analysis of hair shaft. If DNA analysis is combined with microscopic and instrumental analysis in forensic examination, hair individualization can be more accurate. 

Modern DNA profiling is based on the characterization of short tandem repeats (STRs) that are regions (loci) on the chromosome that repeat at least twice within the DNA. For profiling, the number of repeats at each location on the chromosome is determined. To do this, the DNA is first amplified via the polymerase chain reaction (PGR), in which the double-stranded DNA is split into two single strands and a mixture of enzymes and primers are used to replicate specific STR regions of the DNA. In the United States, STRs at thirteen loci are typically considered. The reaction is repeated many times, generating exact copies of the STRs. Because of this... 

The biodistribution of plasmid can be determined by measuring the rate of disappearance of radiolabeled DNA from the bloodstream and its accumulation in tissues or by the use of fluorescence microscopy to trace the leakage of dye-labeled plasmids from the vasculature. Pharmacokinetic analysis of in vivo disposition profiles of radiolabeled plasmid provides useful information on the overall distribution characteristics of systemically administered plasmids, with one critical limitation. The radiolabel represents both intact plasmid and its metabolites. The plasma half-life of plasmid is less than 10 min, and hence tissue distribution and pharmacokinetic parameters of plasmid calculated on the basis of total radioactivity are not valid at longer time points. Thus, polymerase chain reaction and Southern-blot analysis are required to establish the time at which the radiolabel is no longer an index of plasmid distribution. 

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