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A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from 2–5 base pairs) are repeated, typically 5-50 times. Microsatellites occur at thousands of locations in the human genome and they are notable for their high mutation rate and high diversity in the population. Microsatellites and their longer cousins, the minisatellites, together are classified as VNTR (variable number of tandem repeats) DNA. The name "satellite" refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying "satellite" layers of repetitive DNA. Microsatellites are often referred to as short tandem repeats (STRs) by forensic geneticists, or as simple sequence repeats (SSRs) by plant geneticists. They are widely used for DNA profiling in kinship analysis and in forensic identification. They are also used in genetic linkage analysis/marker assisted selection to locate a gene or a mutation responsible for a given trait or disease. ==Structures and Locations== A microsatellite consists of a tract of tandemly repeated (i.e. adjacent) DNA motifs that range in length from two to five nucleotides, and are typically repeated 5-50 times. For example, the sequence TATATATATA is a dinucleotide microsatellite, and GTCGTCGTCGTCGTC is a trinucleotide microsatellite (with A being Adenine, G Guanine, C Cytosine, and T Thymine). Repeat units of four and five nucleotides are referred to as tetra- and pentanucleotide motifs, respectively. The telomeres at the ends of the chromosomes, thought to be involved in senescence, consist of repetitive DNA, with the hexanucleotide repeat motif TTAGGG in vertebrates. They are thus classified as minisatellites, although insects for example have shorter repeat motifs in their telomeres which therefore could arguably be considered microsatellites. Microsatellites are distributed throughout the genome. Many are located in non-coding parts of the human genome and are therefore biologically silent. This allows them to accumulate mutations unhindered over the generations and gives rise to variability which can be used for DNA fingerprinting and identification purposes. Other microsatellites are located in regulatory flanking or intronic regions of genes, or directly in codons of genes - microsatellite mutations in such cases can lead to phenotypic changes and diseases, notably in triplet expansion diseases such as fragile X syndrome and Huntington's disease. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Microsatellite」の詳細全文を読む スポンサード リンク
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