Home >> Science & Nature >> Science

How Does the DNA Barcode Work?

DNA is an abbreviation for deoxyribonucleic acid, the material that transfers genetic characteristics in all forms of life. DNA consists of a double helix, or two coiled chains, of organic molecules, known as nucleotides. Biologists use the sequence of nucleotides to identify different biological species in the same way as supermarkets use computerized barcode labels, bearing a Unique Product Code, to identify different products.

History
- DNA barcoding was first introduced to the scientific community by Paul Hebert of the University of Guelph, Ontario in 2003. Hebert published a paper titled "Biological Identifications Through DNA Barcodes," in which he proposed an approach to identifying and discovering biological species using the same genetic markers -- that is, a DNA barcode -- in each case. According to Paul Hebert himself, the paper is the most heavily cited paper ever published in the Proceedings of the Royal Society.
Technique
- To create a DNA barcode, technicians extracted the DNA from a tiny piece of tissue, isolate the barcode region and use an automated technique, known as polymerase chain reaction amplification, to produce millions of copies of the DNA sequence. They examine the sequence of nucleotides and represent the sequence as a series of letters, C, A, T and G, each representing one of the nucleic acids, cytosine, adenine, thymine and guanine. A sequence of 15 nucleotides, with four options at each position, creates 1 billion possible codes, 100 times more than the total estimated number of animal species. Once created, the DNA barcode is placed into a repository, or reference library, which is used to identify unknown species.
CO1 Gene
- To identify almost all animal groups, including birds, butterflies, fish and flies, biologists examine the sequence of nucleotides in a section of DNA, known as a gene, taken from energy-producing cellular structures called mitochondria. Technically, the gene is known as cytochrome c oxidase 1, or CO1 for short. The CO1 gene is easy to isolate and short enough to be sequenced quickly, but long enough to identify variations between species.
Limitations
- The analogy between DNA barcodes and regular, computerized barcode labels is not entirely consistent because biological species undergo what is known as intraspecific variation, which means that not all the members of a species are identical genetically. Furthermore, while the CO1 gene is highly effective for identifying animal species, it isn't effective for identifying vascular plants, such as ferns and flowering plants, because the gene evolves too slowly.

Science