Short tandem repeat
577431
222996310
2008-07-02T02:40:23Z
Ktr101
5495886
Removed {{Merge|microsatellite|date=April 2007}} as there was one vote against it occuring 8 months ago
A '''short tandem repeat''' (STR) in [[DNA]] is a class of [[polymorphism (biology)|polymorphisms]] that occurs when a pattern of two or more [[nucleotide]]s are repeated and the repeated sequences are directly adjacent to each other. The pattern can range in length from 2 to 10 [[base pair]]s (bp) (for example (CATG)n in a [[genome|genomic region]]) and is typically in the non-coding [[intron]] region, making it [[junk DNA]]. By examining enough STR loci and counting how many repeats of a specific STR sequence there are at a given [[locus (genetics)|locus]], it is possible to create a unique genetic profile of an individual. There are currently over 10,000 published STR sequences in the human genome. STR analysis has become the prevalent analysis method for determining [[Genetic fingerprinting|genetic profiles]] in forensic cases.
==Forensic STR Analysis==
[[Image:Str profile.jpg|thumb|right|400px|A partial human STR profile obtained using the [[Applied Biosystems]] Identifiler kit.]]
STR analysis is a relatively new technology in the field of [[forensics]], having come into popularity in the mid-to-late 1990s. It is used for the [[genetic fingerprinting]] of individuals. The STRs in use today for forensic analysis are all tetra- or penta-nucleotide repeats (4 or 5 repeat units), as these give a high degree of error-free data while being robust enough to survive degradation in non-ideal conditions. Shorter repeat sequences tend to suffer from artifacts such as stutter and preferential amplification, as well as the fact that several genetic diseases are associated with tri-nucleotide repeats such as [[Huntington's disease]]. Longer repeat sequences will suffer more highly from environmental degradation and do not amplify by [[polymerase chain reaction|PCR]] as well as shorter sequences.
The analysis is performed by extracting [[nuclear DNA]] from the cells of a forensic sample of interest, then amplifying specific [[polymorphism (biology)|polymorphic]] regions of the extracted DNA by means of the [[polymerase chain reaction]]. Once these sequences have been amplified, they are resolved either through [[gel electrophoresis]] or [[capillary electrophoresis]], which will allow the analyst to determine how many repeats of the STR sequence in question there are. If the DNA was resolved by gel electrophoresis, the DNA can be visualized either by [[silver stain]]ing (not very high resolution, safe, inexpensive), or an [[DNA intercalation|intercalating dye]] such as [[ethidium bromide]] (fairly sensitive, moderate health risks, inexpensive), or as most modern forensics labs use, [[Fluorescence|fluorescent dyes]] (highly sensitive, safe, expensive). Instruments built to resolve STR fragments by capillary electrophoresis also use fluorescent dyes to great effect. It also used to follow up [[bone marrow transplant]] patients.
In the [[United States]], 13 core STR [[locus (genetics)|loci]] have been decided upon to be the basis by which an individual genetic profile can be generated. These profiles are stored on a local, state and national level in DNA databanks such as [[CODIS]]. The [[United Kingdom|British]] data base for STR loci identification is the [[UK National DNA Database]] (NDNAD). The British system uses 10 loci, rather than the American 13 loci.
[[Y-STR]]s (STRs on the [[Y chromosome]]) are often used in [[genealogical DNA test]]ing.
==See also==
*[[tandem repeat]]
*[[variable number tandem repeat]]
*[[nucleotide sequence]]s
*[[Microsatellite]]
*[[Minisatellite]]
*[[Y-STR]]
*[[List of DYS markers]]
*[[Genetic fingerprinting]]
==External links==
*[http://www.gendna.net/ydnacomp.htm Y-DNA Testing Company STR Marker Comparison Chart]
*[http://www.str-base.org/ ENFSI STR Population Database]
*[http://www.cstl.nist.gov/biotech/strbase/index.htm National Institute of Standards and Technology (NIST)] — STR database
*[http://www.cstl.nist.gov/div831/strbase/str_fact.htm National Institute of Standards and Technology (NIST)] — STR Fact Sheets
[[Category:Repetitive DNA sequences]]
[[Category:Genetic genealogy]]
[[Category:DNA profiling techniques]]
[[de:Short tandem repeat]]
[[es:SSR]]