An Idiots Guide to DNA barcoding - 3.

The total number of unique organisms described to the species level is around 1.5 million, but the total number of "species" is likely to be in the region of 10 million. The overall "taxonomic deficit" (the ratio of expected taxa to named taxa) is thus approximately sixfold. For vertebrates, the current described species total is likely to be relatively close to the "true" total: we have described most of these relatively large organisms. The same is true of most groups whose members have body sizes greater than 10 mm. However, the vast majority of organisms on the Earth have body sizes less than 1 mm, and for these groups the taxonomic deficit is likely to be several fold worse than for land plants and vertebrates. These meio- and micro-fauna and flora are, however, key to the functioning of ecosystems and are the productive base upon which the macro-organisms rely. Their size precludes facile visual identification, and indeed much of their important morphology may be at scales that are beyond the resolution of light microscopy. Wendell Berry quotes from his daughter in his poem: To the unseeable animal: "I hope there's an animal somewhere that nobody has ever seen. And I hope nobody ever sees it.". DNA barcoding may permit rational access to these animals

 

Molecular Evolution Studies and DNA barcoding:

With the advent of DNA sequencing technology in the 1970s, it became possible to study the evolution and evolutionary relatedness of species through the relative similarity of their gene sequences. Closely related organisms generally have a high degree of seuqnece similarity, while the molecules of organisms distantly related usually show a pattern of dissimilarity. Molecular phylogeny uses such data to build a "relationship tree" that shows the probable evolution of various organisms (see figure).

Molecular phylogeney has clarified many uncertainties in our view of species relationships and is particularly important in the study of evolutionary relationships between small and microscopic organisms (such as some insects, nematodes, protozoa and bacteria) which are vitaly important for ecosystems but where morphological features are difficult to identify and compare.