A short tandem repeat (STR or microsatellite) is a pattern of two or more nucleotides that are repeated directly adjacent to each other. The repeats can range in length from 2 to 6 base pairs/repeat. A short tandem repeat polymorphism occurs when homologous STR loci differ in the number of repeats between individuals. By identifying repeats of a specific sequence at specific locations in the genome, it is possible to create a genetic profile of an individual. When running a QF-PCR assay, STRs are amplified by PCR using the unique sequences of flanking regions as primers. By using fluorescently labeled primers amplified STRs can be identified and quantified on a capillary electrophoresis instrument.