A microsatellite is a short, noncoding DNA sequence (a Tandemly Repetitive DNA sequence) that is repeated many times within the genome of an organism. Many repeats tend to be concatenated at the same locus.
In a microsatellite, the repeated sequence is very simple, consisting of from two to four nucleotides, and can be repeated 10 to 100 times. Hence if one sequenced a microsatellite locus, one would expect to see a sequence of "TAGTAGTAGTAGTAGTAGTAG..."
The number of repeats at a particular locus is hypervariable (highly polymorphic) between individuals of the same species. It is for this reason that microsatellite sequences can be used for genetic fingerprinting and paternity testing. Most loci of the genome, even non-coding parts, would be too similar to allow individuals to be reliably distinguished.
The hypervariability arises because the repeated simple sequences cause a high frequency of loss or insertion of additional repeats by confusing the DNA replication machinery. Self-complementary sequences may aid this process.
In tumour cells, where controls on replication may be damaged, microsatellites may be gained or lost at an especially high frequency during each round of mitosis. Hence a tumour cell line might show a different genetic fingerprint from that of the host tissue.
Testing for microsatellite instability helps doctors determine whether a person is likely to have a gene mutation that causes hereditary nonpolyposis colorectal cancer (also known as HNPCC or Lynch Syndrome).
Tests are available that detect microsatellite instability in tumor cells, and finding numerous longer or shorter microsatellite regions in these cells suggests the presence of a mutated DNA mismatch repair gene — and that in turn points to HNPCC.
If a patient's tumor cells show no evidence of microsatellite instability, it's unlikely that he or she has a mutated mismatch repair gene — and that's precisely what genetic tests for HNPCC are looking for.
Microsatellites are defined as short patterned non-coding regions containing specific genetic sequences that are repeated one right after the other (in direct sequence) within the genome of an organism.
The repeated sequence in a microsatellite consists of two, three or four nucleotides (di-, tri-, or tetra-nucleotide repeats respectively) and can be repeated many times (upwards of 100).
During the analysis of microsatellites in humans and other organisms it has become evident that the number of repeated sequences in a particular microsatellitelocus can vary (location on the chromosome).
Feeds |
Contact