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Not to be confused with the DNA barcode involved in optical mapping of DNA.



 

DNA barcoding is a method of species identification and discovery using a short section of DNA from a specific gene or genes. That DNA sequence can be used to identify different species; in the same way a supermarket scanner uses the familiar black stripes of the UPC barcode to identify your purchases. These "barcodes" are sometimes used in an effort to identify unknown species, parts of an organism, or simply to catalog as many taxa as possible.

Different gene regions are used to identify the different organism groups using barcoding. The most commonly used barcode region for animals and some protists is a portion of the cytochrome oxidase I (COI or COX1) gene found in mitochondrial DNA. Microorganisms are detected using different gene regions, for example 16S RNA is widely used in identification of prokaryotes. These gene regions are chosen because they have less infraspecific (within species) variation than interspecific (between species) variation, which is known as the "Barcoding Gap".

Applications of DNA barcoding include: identifying plant leaves even when flowers or fruit are not available, identifying pollen collected on the bodies of pollinating animals or identifying insect larvae which may have fewer diagnostic characters than adults. When barcoding is used to identify a wide range of organisms from the same sample the term DNA metabarcoding is used, e.g. DNA metabarcoding of diatom communities in rivers and streams, which allow the estimation of the quality status.

Background
DNA barcoding techniques were developed from the early DNA sequencing work carried out by Carl Woese, Mitchell Sogin and Stephen Sogin on microbial communities using the 5S rRNA gene. In 2003, the specific methods and terminology of modern DNA barcoding were proposed as a standardized method for identifying species, as well as potentially allocating unknown sequences to higher taxa such as orders and phyla, in a paper by Paul D.N. Hebert et al. from the University of Guelph, Ontario, Canada. Hebert and his colleagues demonstrated the utility of the cytochrome c oxidase I (COI) gene, first utilized by Folmer et al. in 1994, using their published DNA primers as a tool for phylogenetic analyses at the species levels, as a suitable discriminatory tool between metazoans.The study authors created a COI "profile" for eight of the most diverse orders of insects, based on a single representative from each of 100 different families, and showed that this profile assigned each of 50 newly analysed taxa to its correct order.

Calling the profiles "barcodes", Hebert et al. envisaged the development of a COI database that could serve as the basis for a "global bioidentification system", and wrote: "When fully developed, a COI identification system will provide a reliable, cost-effective and accessible solution to the current problem of species identification. Its assembly will also generate important new insights into the diversification of life and the rules of molecular evolution."

The "Folmer region" of the COI gene is commonly used to distinction taxa based on its patterns of variation at the DNA level, the relative ease of retrieving the sequence, and variability mixed with conservation between species. Global DNA barcoding was initially regarded as a "big science" programme and even as the renaissance of taxonomy.