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 labelled primers amplified STRs can be identified and quantified on a capillary electrophoresis instrument.
Stutter peaks from STR markers
Stutter peaks are peaks that may be detected primarily one repeat shorter than the true allele. They appear as a result of strand slippage during DNA synthesis. Stutter is less pronounced with larger repeat unit sizes (di- > tri- > tetra repeats). Devyser’s QF-PCR kits include only tetra repeat STRs and the STRs have been carefully selected to provide maximum informativity while generating minimal amount of stutter products.