WRITTEN in the DNA of every animal is a unique barcode that could let taxonomists identify every animal on the planet with unprecedented ease.
The barcode is written on a mitochondrial gene, which is found in all aerobic life, that codes for a protein called cytochrome c oxidase I. The new method should make life easier for scientists trying to assess biodiversity.
Conventional taxonomy has hit a bottleneck because it demands expert anatomical comparisons of complete animal specimens. It has taken 250 years to classify about one million animal species 鈥� about 10 per cent of the global total, says Paul Hebert of the University of Guelph in Ontario.
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Hebert convened a workshop at the Cold Spring Harbor Laboratory in New York State last week after suggesting earlier this year (Proceedings of the Royal Society B, vol 270, p 313) that certain DNA sequences are as good as barcodes and would be a more practical way of identifying species.
Other groups already use extensive sequences of DNA to study broad relationships among animal groups, such as the 鈥淭ree of Life鈥� programme begun last year (快猫短视频, 9 November 2002, p 7). Resolving deep relationships among the branches requires a lot of data, says Hebert.
The aim is to develop an analytical tool so powerful that with an afternoon鈥檚 training, you could identify any species in the databank of barcodes. Cataloguing biodiversity in poorly studied regions is only one use for the barcode. Because DNA analysis requires only a few cells, a sample of undigested blood would be enough to identify the species a mosquito had fed on 鈥� a key issue with diseases like West Nile virus.
The gene Hebert has homed in on resides in the mitochondria 鈥� the cell鈥檚 energy source 鈥� which have only 13 protein-coding genes and no introns, stretches of DNA that don鈥檛 appear to code for any proteins. That makes mitochondrial genes simpler to sequence than the far more abundant genes in the cell鈥檚 nucleus. But only two of these genes are common throughout the animal kingdom 鈥� and the technology for sequencing COI 鈥� the cytochrome c oxidase I gene 鈥� is further advanced.
You can identify individual species with the barcode because DNA sequences in genes vary much more than the amino acid sequences in the proteins they code for. For example, human and chimpanzee versions of cytochrome c oxidase I differ by only one amino acid, but the DNA in the COI gene differs by 75 base pairs.
Using the DNA barcode technique, Hebert has already identified some 500 species of moths and butterflies, and plans to test another 500 by the end of the year. He says making a global inventory of animal life would cost up to $2.5 billion 鈥� and take up to 20 years.