Species Identification Threshold
Definition
The minimum sequence similarity percentage at which a database match is accepted as a species-level assignment. Forensic laboratories typically require 98 to 99 percent similarity to the closest reference sequence for a definitive species call. Below this threshold, the result is reported at genus or family level only.
- Field
- DNA barcoding, molecular identification
- Typical threshold
- 98 to 99 percent sequence similarity
- Below threshold result
- Reported at genus or family level only
- Depends on
- Marker choice and reference database coverage
Common questions
Why not just report the closest match regardless of similarity percentage?+
A close but sub-threshold match can reflect a related species missing from the reference database rather than a true identification, so labs cap the claim at genus or family level to avoid overstating certainty.
Does a fixed threshold work equally well across all taxonomic groups?+
No. Natural sequence divergence between closely related species varies by group, so a single similarity cutoff can be too strict for some taxa and too lenient for others, which is a known limitation of barcode-only identification.
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...
- COI (Cytochrome Oxidase Subunit I)
- The primary barcode gene for the animal kingdom under the Barcode of Life initiative. A 648-bp region within the COI gene is...
- 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
- Species identification using a short, standardised region of the mitochondrial genome. For animals, the primary barcode marker is a 648-base-pair segment of...