What is DNA Barcoding?

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DNA Barcoding: combining morphological and molecular identification methods.

Identifying the millions of species on earth that have yet to be described is a monumental task that will require analysis of differences between organisms. Characteristics that differ between organisms are used to group organisms into separate species. Two general rules when classifying any group of organisms are: 1) the greater the number of characteristic differences, the greater the liklihood any two organisms are separate species; and 2) the greater the number of characters observed, the greater the reliability of the classification. Characters such as morphology, behavior, and distribution have historically been used to identify organisms as species groups. More recently DNA technology has added additional characters (differences in DNA sequences) to the database of information on species groups. In concert with traditional taxonomic techniques for identifying species, DNA sequence techniques provide a powerful tool for recognizing differences and similiarities among species.

“In 2003, researchers at the University of Guelph in Ontario, Canada, proposed “DNA barcoding” as a way to identify species. Barcoding uses a very short genetic sequence from a standard part of the genome the way a supermarket scanner distinguishes products using the black stripes of the Universal Product Code. Two items may look very similar to the untrained eye, but in both cases the barcodes are distinct.

Until now, biological specimens were identified using morphological features. In some cases a trained technician could make routine identifications using morphological “keys”, but in most cases an experienced professional taxonomist is needed. If a specimen is damaged or is in an immature stage of development, even specialists may be unable to make identifications. Barcoding solves these problems, because non-specialists can obtain barcodes from tiny amounts of tissue. This is not to say that traditional taxonomy has become less important, but rather that DNA barcoding can serve a dual purpose as a new tool in the taxonomists toolbox supplementing his/ her knowledge as well as being an innovative device for non-experts who need to make a quick identification.” http://www.barcoding.si.edu/whatis.html

The barcode region used for the identification of animals is located on a protein-coding gene found in mitochondria called Cytochrome Oxidase 1 (CO1). CO1 is a component of the electron transport apparatus essential to all aerobically respiring organisms. One advantage of using mitochondrial genes, rather than nuclear genes, resides in the fact that mitochondria are present in multiple copies per cell and it is easier to acquire DNA products through polymerase chain reactions. Another advantage is that mitochonrial genomes evolve faster and have greater DNA sequence differences between species than nuclear genes. This poses a potential problem though when one considers differences within species. Fortunately differences between species (interspecific variation) are much greater than differences within species (intraspecific variation). A proposed standard for the identification of species groups is a “barcoding gap” defined as 10x the intraspecific variation.

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