DNA barcoding

A supermarket can tell a thousand products apart in an instant by scanning a single short barcode on each — no need to inspect the whole item. DNA barcoding brings that idea to living things: instead of being an expert who recognizes a species by examining its whole body, you read one short, standardized stretch of its DNA and match it against a reference library to name the species.

The method picks a short gene region that is two things at once: similar enough within a species that all individuals share nearly the same sequence, yet different enough between species that each species has its own distinct version. For animals, the standard barcode is a roughly 650-letter piece of the mitochondrial gene cytochrome c oxidase I (often written COI); plants and fungi use other regions because COI varies too little in them. In practice you take a tiny sample — a leg from an insect, a scrap of meat, a swab of pond water — amplify the barcode region with PCR, sequence it, and look up the closest match in a curated database such as the Barcode of Life library. If the match is good, you have an identification, even from a fragment that no expert could recognize by eye.

DNA barcoding is molecular phylogenetics put to everyday work. It identifies insect larvae that look identical, exposes seafood fraud (cheap fish sold as expensive species), screens for endangered species in illegal trade, and, in its 'metabarcoding' form, reads all the species in a scoop of soil or water at once to survey biodiversity. The honest limits matter: a barcode names species but does not by itself build a reliable deep family tree; closely related or recently split species can share barcodes; and the answer is only as good as the reference library, which is incomplete and can contain mislabeled entries.