Genomic STR GenotypingDNA profiling technologies >> Technological Solution >>STRs are a specific type of repetitive DNA sequences occupying about 3% of the human genome. STRs represent a rich source of highly polymorphic DNA markers, because of the instability of these sequences during cell meiosis and mitosis. These markers are usually detected using the PCR (polymerase chain reaction). Alleles of STR loci are differentiated by the number of copies of the repeat sequence contained within the amplified region, and are usually distinguished from one another using fluorescence detection following separation by capillary electrophoresis. The advantages of STR genotyping are various. One is that STR genotyping is more tolerant of the use of degraded DNA than other typing methods, because the amplification products are less than 500 bp long. STR products are of discrete and separable lengths, and this allow construction of allelic ladders containing fragments of the same lengths as several or all known alleles for each locus, thus providing rapid and precise assignment of alleles. The genomic STR genotyping method has been chosen to generate the main and pioneering application of the DNA tracing technologies, the so-called DNA fingerprinting or simply DNA test for human individuality. Two standards have been set for this analysis. The first is the CODIS, proposed in the US by the Federal Bureau of Investigation, and adopting 13 STR loci. Recently European autorities introduced as European standard an improved version of CODIS, with 15 STR loci.
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