Skip to content Skip to navigation Skip to collection information

OpenStax-CNX

You are here: Home » Content » DNA Barcodes Decoded » Current Research: DNA Barcode Synopsis

Navigation

Recently Viewed

This feature requires Javascript to be enabled.
 

Current Research: DNA Barcode Synopsis

Module by: Alison Fromme. E-mail the author

Summary: Is it possible to identify species using a standard piece of DNA? Liza Gross summarizes original research published by PLoS Biology that investigates this question.

hebert-synopsis.bmp

One hundred years before Darwin returned from his voyage on the H. M. S. Beagle “struck with certain facts” that “seemed to throw some light on the origin of species,” Linnaeus published the first systematic taxonomy of life. In Systema Naturae, the Swedish botanist divided organisms into plants, animals, and minerals, eventually assigning scientific names to 7,700 plant and 4,400 animal species, and popularizing the binomial system—as in Homo sapiens—of naming species.

In the 1700s and 1800s, naturalists classified organisms based on morphology, devoting their careers to naming newfound plants and animals. Today biologists still use Linnaean taxonomy as the foundation of scientific classification. But with just a fraction of the estimated 5–30 million species on the planet already named and too few specialists to do the job, biologists are looking for high-throughput tools that can rapidly and accurately identify both individuals of a species and entirely new species. That's what some scientists say the DNA barcode will do. The DNA barcode, as the name implies, uses genes to identify species much like supermarket barcodes identify products. The idea is that a short stretch of genetic code from a reference gene is unique enough to one species to distinguish it from every other species, and that comparisons of sequence variations in that stretch of gene can reveal evolutionary relationships among species.

Such technology could radically advance biologists' attempts to achieve the long-standing goal of cataloging life on earth, but the approach is controversial, with critics questioning both the method and its applications. (For more on the debate, see “DNA Barcoding: Promise and Pitfalls”.) Paul Hebert and colleagues offer a proof of the utility of the DNA barcoding concept, using a 648-basepair region of a mitochondrial gene (cytochrome c oxidase I, or COI) in a study of 260 North American bird species.

Mitochondria—the cell's power generators—contain their own DNA, and mitochondrial DNA (mtDNA) evolves much faster than nuclear DNA. It evolves so quickly, in fact, that mtDNA sequence variation has been found not just between closely related, or sister, species but also within species. Still, the variation is much greater among than within species, which is why mtDNA divergences have become a tool for identifying species.

Hebert and colleagues tested the effectiveness of the mtDNA COI barcode by matching bird species flagged by the COI barcode against those already established by taxonomic methods. The litmus test for DNA barcoding is absence of COI sequence overlap between species. Beyond that, differences within species should be significantly fewer than those between species. And that's what the researchers found. All 260 species had unique COI barcodes, with differences between species for the most part much more frequent—on average, 18 times more common—than those within species. In the 130 species represented by two or more individuals, COI sequences were either identical or closest to other sequences within that species. For these 260 bird species (of the 667 bird species that breed in North America), the authors report, the COI barcodes “separate individuals into the categories that taxonomists call species.”

The COI barcode, the authors propose, could help resolve problematic classifications based on morphology, as arise when populations of a single species acquire distinct characteristics after geographic barriers prevent their interbreeding. For example, the similar COI sequences found in American and black oystercatchers here support taxonomic studies suggesting that they are actually color morphs of one species. And conversely, highly divergent COI sequences might bolster taxonomic studies indicating that lineages of uncertain status are indeed distinct species.

Future studies will have to determine whether these results can be generalized to animals in other climes and ecosystems, but the authors argue that constructing a comprehensive library of barcodes will facilitate such efforts. Hebert and colleagues conclude that the success of DNA barcoding depends not only on such a repository—with sequences pegged to well-characterized species exemplars—but also on the expertise of trained taxonomists. The hope is that large-scale, standardized testing based on a uniform barcode sequence could go a long way toward finishing what Linnaeus started: a full classification of all plant and animal life. To E. O. Wilson, every species is “a masterpiece of evolution, offering a vast source of useful scientific knowledge because it is so thoroughly adapted to the environment in which it lives.” Faced with what Wilson calls the “worst wave of extinction since the dinosaurs died,” the need for a fast and easy way to identify species has never been greater.

Source

Citation: (2004) A Test Case for DNA Barcodes to Identify Species. PLoS Biol 2(10): e357.

DOI: 10.1371/journal.pbio.0020357

Published September 28, 2004

Copyright: © 2004 Public Library of Science. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Collection Navigation

Content actions

Download:

Collection as:

PDF | EPUB (?)

What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

Downloading to a reading device

For detailed instructions on how to download this content's EPUB to your specific device, click the "(?)" link.

| More downloads ...

Module as:

PDF | More downloads ...

Add:

Collection to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks

Module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

Definition of a lens

Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

Who can create a lens?

Any individual member, a community, or a respected organization.

What are tags? tag icon

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks