DNAbarcoding

DNA barcoding is a method for identifying species using a short, standardized region of DNA. For animals, the most commonly used barcode is a ~650 base pair fragment of the mitochondrial gene cytochrome c oxidase I (COI). In plants, barcode markers typically include the chloroplast genes rbcL and matK, while fungi commonly use the nuclear ribosomal internal transcribed spacer (ITS) region. The goal is to assign an unknown specimen to a species by comparing its barcode sequence to a reference library of authenticated sequences.

DNA barcoding relies on the existence of a robust reference database, such as the Barcode of Life Data Systems (BOLD) or public GenBank records. The standard workflow involves collecting a specimen, extracting DNA, amplifying the barcode region by PCR, sequencing the amplicon, and matching the sequence against the reference library using similarity thresholds or phylogenetic methods. When a close match is found, the specimen is identified to species; when matches are ambiguous, higher taxonomic levels or multiple loci may be used.

Applications of DNA barcoding include rapid biodiversity assessments, species discovery and inventory projects, food authentication and forensics, ecological and environmental monitoring, and detection of invasive species. It is also used in conservation planning and regulatory frameworks where rapid identification is valuable. Limitations include dependence on comprehensive reference libraries, limited resolution for recently diverged or morphologically cryptic species, intra-specific variation, geographic structure, presence of nuclear copies or sequencing errors, and challenges with degraded or mixed DNA samples. Barcode data should be interpreted alongside traditional taxonomic methods.

DNA barcoding is a foundational component of broader DNA-based identification approaches, such as DNA metabarcoding, and remains a subject of ongoing refinement, with debates about standardization, thresholds, and the need for multi-locus or integrative taxonomy to improve species delimitation.