COI (Cytochrome Oxidase Subunit I)
Definition
The primary barcode gene for the animal kingdom under the Barcode of Life initiative. A 648-bp region within the COI gene is the official BOLD barcode. COI is less used in vertebrate forensic work than cytochrome b but is standard for invertebrates, fish, and many other taxa.
- Standard region
- 648 bp BOLD barcode
- Coordinating initiative
- Barcode of Life
- Strongest use
- Invertebrates, fish, and many non-vertebrate taxa
- Comparison
- Less used than cytochrome b for vertebrate forensic work
Common questions
Why is cytochrome b preferred over COI for some vertebrate forensic identifications?+
Cytochrome b has an established reference database and validated primer sets specifically built up around vertebrate forensic and wildlife casework over a longer period, so laboratories doing vertebrate species work often default to it even though COI could technically be used.
In what casework does COI outperform cytochrome b?+
For invertebrates, fish, and many non-vertebrate taxa, COI has the deeper and more standardised BOLD reference library, so a query sequence is more likely to match a curated entry than it would against cytochrome b databases built mainly around vertebrates.
Related terms
- BOLD (Barcode of Life Data System)
- A curated online reference database of barcode sequences maintained by the University of Guelph, Canada. Each entry includes a voucher specimen, taxonomic...
- CITES
- The Convention on International Trade in Endangered Species of Wild Fauna and Flora, a multilateral treaty signed in 1973 now with over...
- Cytochrome B (Cyt B)
- A mitochondrial protein-coding gene widely used in forensic species identification before COI barcoding was standardised. Still used because its reference database for...
- DNA Barcoding
- Taxonomic identification using sequence information from selected genomic regions compared with appropriate references. Resolution depends on the markers, taxa, specimen and database;...
- Species Identification Threshold
- The minimum sequence similarity percentage at which a database match is accepted as a species-level assignment. Forensic laboratories typically require 98 to...