Simple Sequence Repeats (SSR): Microsatellites
Microsatellites, also called simple sequence repeats (SSR), are sequences present in the genomes and are used very often as molecular markers because of their simplicity and wide distribution in genomes of eukaryotic species. They are made up of tandem repeats of a simple DNA motif (a few nucleotides). The motifs may be mono-, di-, tri-, or tetranucleotides, for example CA repeated n times for a dinucleotide microsatellite. The peculiarity of microsatellites arises from their use in the search for polymorphism between individuals. This polymorphism does not lie in the sequence itself (CA dinucleotides are present in all genomes) but in the number of repetitions of these simple motifs. For example, at a given locus of a genome, an individual A will have 15 repeats of motif CA, while individual B will have 18 repeats of the same motif.