A short tandem repeat (STR) in DNA is a class of polymorphisms that occurs when a pattern of two or more nucleotides are repeated and the repeated sequences are directly adjacent to each other. The pattern can range in length from 2 to 10 base pairs (bp) (for example (CATG)n in a genomic region) and is typically in the non-coding intron region, making it junk DNA. By examining several STR loci and counting how many repeats of a specific STR sequence there are at a given 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 profiles in forensic cases. The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ... In biology, polymorphism can be defined as the occurrence in the same habitat of two or more forms of a trait in such frequencies that the rarer cannot be maintained by recurrent mutation alone. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... In molecular biology, two nucleotides on opposite complementary DNA or RNA strands that are connected via hydrogen bonds are called a base pair (often abbreviated bp). ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... Diagram of the location of introns and exons within a gene. ... In molecular biology, junk DNA is a collective label for the portions of the DNA sequence of a chromosome or a genome for which no function has yet been identified. ... In biology and evolutionary computation, a locus is the position of a gene (or other significant sequence) on a chromosome. ... Genetic fingers, DNA testing, DNA typing, and DNA profiling are techniques used to distinguish between individuals of the same species using only samples of their DNA. Its invention by Sir Alec Jeffreys at the University of Leicester was announced in 1985. ...

Forensic STR Analysis

STR analysis is a relatively new technology in the field of forensics, having come into popularity in the mid-to-late 1990's. 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 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 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 staining (not very high resolution, safe, inexpensive), or an intercalating dye such as ethidium bromide (fairly sensitive, moderate health risks, inexpensive), or as most modern forensics labs use, fluorescent dyes (highly sensitive, safe, expensive). Instruments built to resolve STR fragments by capillary electrophoresis also use fluorescent dyes to great effect. Nuclear DNA is DNA contained within a nucleus of eukaryotic organisms. ... In biology, polymorphism can be defined as the occurrence in the same habitat of two or more forms of a trait in such frequencies that the rarer cannot be maintained by recurrent mutation alone. ... Polymerase chain reaction (PCR) is a molecular biology technique [1] for enzymatically replicating DNA without using a living organism, such as E. coli or yeast. ... Gel electrophoresis is a group of techniques used by scientists to separate molecules based on physical characteristics such as size, shape, or isoelectric point. ... Capillary electrophoresis (CE) can be used to separate ionic species by their charge and frictional forces. ... Silver staining is the use of silver to stain histologic sections. ... Intercalation induces structural distortions. ... Ethidium bromide (EtBr) is an intercalating agent commonly used as a nucleic acid stain in molecular biology laboratories for techniques such as agarose gel electrophoresis. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ...

In the United States, 13 core STR 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. In biology and evolutionary computation, a locus is the position of a gene (or other significant sequence) on a chromosome. ... The Combined DNA Index System (CODIS) is the FBIs national databases of genetic identification codes. ...

Y-STRs (STRs on the Y chromosome) are often used in genealogical DNA testing. A Y-STR is a short tandem repeat (STR) on the Y chromosome. ... The human Y chromosome is one of two sex chromosomes, it contains the genes that cause testis development, thus determining maleness. ... // A genealogical DNA test involves examining the nucleotides at specific locations on a persons DNA. The tests results are meant to have no informative medical value and do not determine specific genetic diseases or disorders (see possible exceptions in Medical information below); they are intended only for use in...

See also

• tandem repeat
• variable number tandem repeat
• nucleotide sequences
• Microsatellite
• Minisatellite
• Y-STR
• List of DYS markers
• Genetic fingerprinting

The British data base for STR loci identification is The National DNA Data Base (NDNAD) compared to the American CODIS system the British system uses 10 loci not 13 loci. This is a term from genetics, which describes a pattern that helps determine an individuals inherited traits. ... A variable number tandem repeats (VNTR) is a short nucleotide sequences ranging from 14 to 100 nucleotides long that is organized into clusters of tandem repeats. ... A DNA sequence (sometimes genetic sequence) is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, The possible letters are A, C, G, and T, representing the four nucleotide subunits of a DNA strand (adenine, cytosine, guanine, thymine), and typically these are... Microsatellites, or Simple Sequence Repeats (SSRs), are polymorphic loci present in nuclear DNA that consist of repeating units of 1-4 base pairs in length [1]. They are typically neutral, co-dominant and are used as molecular markers which have wide-ranging applications in the field of genetics, including kinship... Minisatellites consist of repetitive, generally GC-rich, variant repeats that range in length from 10 to over 100 bp. ... A Y-STR is a short tandem repeat (STR) on the Y chromosome. ... The following DYS markers are commonly tested in genealogical DNA testing. ... Genetic fingers, DNA testing, DNA typing, and DNA profiling are techniques used to distinguish between individuals of the same species using only samples of their DNA. Its invention by Sir Alec Jeffreys at the University of Leicester was announced in 1985. ...

External links

• National Institute of Standards and Technology (NIST) — STR Fact Sheets

A partial human STR profile obtained using the Applied Biosystems Identifiler kit.