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. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Polymorphism in biology occurs when two or more clearly different Phenotypes exist in the same population of a species — in other words the occurrence of more than one Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group 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. In Molecular biology, two Nucleotides on opposite complementary DNA or RNA strands that are connected via Hydrogen bonds are called In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into In Molecular biology, junk DNA is a provisional label for the portions of the DNA sequence of a Chromosome or a Genome for which no By examining enough 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. In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a 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.

Forensic STR Analysis

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. Huntington's disease, also called Huntington's chorea, chorea major, or HD, is a genetic neurological disorder characterized after 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. Nuclear DNA, nuclear deoxyribonucleic acid (nDNA is DNA contained within a nucleus of eukaryotic organisms. Polymorphism in biology occurs when two or more clearly different Phenotypes exist in the same population of a species — in other words the occurrence of more than one 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. Capillary electrophoresis ( CE) also known as capillary zone electrophoresis (CZE can be used to separate ionic species by their charge and frictional forces 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). Silver staining is the use of Silver to stain Histologic sections This kind of staining is important especially to show Proteins (for example type III In Chemistry, intercalation is the reversible inclusion of a Molecule (or group between two other molecules (or groups Ethidium bromide (sometimes abbreviated as "EtBr", the abbreviation also confusingly used for Bromoethane) is an intercalating agent Fluorescence is a Luminescence that is mostly found as an 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 loci have been decided upon to be the basis by which an individual genetic profile can be generated. The United States of America —commonly referred to as the In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a These profiles are stored on a local, state and national level in DNA databanks such as CODIS. The Combined DNA Index System (CODIS is a DNA database funded by the United States Federal Bureau of Investigation (FBI The British data base for STR loci identification is the UK National DNA Database (NDNAD). The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located The British system uses 10 loci, rather than the American 13 loci.

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. Y-STRs are often designated by DYS numbers. The Y chromosome is the sex-determining Chromosome in most Mammals including Humans In mammals it contains the gene SRY, which triggers A genealogical DNA test examines the Nucleotides at specific locations on a person's DNA for Genetic genealogy purposes

See also

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

External links

• Y-DNA Testing Company STR Marker Comparison Chart
• ENFSI STR Population Database
• National Institute of Standards and Technology (NIST) — STR database
• National Institute of Standards and Technology (NIST) — STR Fact Sheets