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Chromosomal sites that contain repeats of a small number of nucleotides arranged one after the other. The tandemly repeated motif usually contains between one and six nucleotides. Microsatellites are also called short tandem repeats (STRs). Microsatellites have been found in every species studied so far. They are evenly distributed along the chromosomes, but are rare within coding sequences. During the replication of chromosomal segments containing tandem repeats, the nascent DNA strand may separate from the template strand and then reanneal so that it is out of phase with the template. When replication resumes, the newly completed strand will be longer or shorter than the template depending on whether the looped-out bases occurred in the template or the nascent strand. Such slippage strand mispairing during the replication of microsatellites is the main mechanism for increasing the length of microsatellites. Some human diseases are caused by expaning the length of trinucleotide repeats (q.v.). See genetic instability, STR analysis.

Subjects: Genetics and Genomics — Chemistry.

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