The ideal barcoding gene
A gene from mitochondria, called cytochrome c oxidase subunit 1 (CO1), was selected by the Consortium for the Barcode of Life (CBOL) as the ideal gene for DNA barcoding animal species.
What makes the CO1 gene an ideal barcoding gene?
It’s an essential gene
The CO1 gene codes for a protein that has an essential role in cellular respiration.
Mitochondrion electron micrograph
An electron micrograph showing a mitochrondrion inside a rat cell. The mitochondrion has a double outer membrane and folded inner membrane called cristae.
Cellular respiration breaks down food molecules, like glucose, to release carbon dioxide and water. It’s how the cell generates energy.
It’s present in many living things
The CO1 gene is present in most eukaryotes.
This gene is highly conserved across species where energy is generated from mitochondria. Because the gene is highly conserved, it can be copied from unknown organisms.
Each cell contains many identical copies
The CO1 gene is a mitochondrial gene.
Each cell has many mitochondria (from 1-1000 copies depending upon how much energy the cell needs), each one containing multiple copies of mitochondrial DNA. When tissue sample is limited, this means that you’ve got a good chance of extracting enough mitochondrial DNA for successful PCR.
For further information, see article: More about mitochondria.
Close enough but not too close
For DNA barcoding of animals, the CO1 gene can be used to identify individuals belonging to the same species, as well as to distinguish between individuals from different species. This is because the rate that the gene sequence changes over time is slow enough so that it’s likely to be identical in the same species, but fast enough so that it’s different between species.
For further information, see article: Barcoding New Zealand swamp hens.
Problems with the ideal gene?
DNA barcoding is a new and exciting field, with many developments in the last 5 years. There are, however, some recognised challenges to using the CO1 gene:
Fake copies of the gene or pseudogenes – copies of mitochondrial genes are sometimes transferred from mitochondrial DNA to nuclear DNA during evolution. Scientists may unintentionally amplify and sequence these nuclear pseudogenes.
Not an ideal gene for barcoding plants – while mitochondria are present in plants, the sequence of the plant CO1 gene doesn’t change much. This means that it can’t be used for DNA barcoding. The search is on for a gene or genes that will allow plant DNA to be barcoded.
