DNA Barcode

DNA Barcoding

DNA barcoding is a novel taxonomic method that uses a short genetic sequence in an organism's genome to identify it as belonging to a specific species. It differs from molecular phylogeny in that the main goal is not to determine patterns of relationship but to identify an unknown sample in terms of a preexisting classification. Since it is an accurate, inexpensive and effective technique without the experiences of experts, which makes the authentication of species accessible to non-specialists. Although barcodes are sometimes used in an effort to identify unknown species or assess whether species should be combined or separated, the utility of DNA barcoding for these purposes is subject to debate.

Exonn has involved in the design and development of DNA barcode analysis for species authentication services. We focus on providing the best possible DNA barcode service for all life forms led us to establish standard protocols. Our range of service for DNA Barcoding of animals, insects, plants, Algae, Fungi, Bacteria, and Seaweeds covers sample to database submission.

Animals and Insects DNA Barcoding

All eukaryote cells contain mitochondria, and animal mitochondrial DNA (mtDNA) has a relatively fast mutation rate, resulting in the generation of diversity within and between populations over relatively short evolutionary timescales. This contrasts with the nuclear genome, which is around 100 000 times larger, where males and females each contribute two full genomes to the gene pool and effective size is therefore proportional to twice the total population size. A 658-bp region of the mitochondrial cytochrome c oxidase subunit I (COI or COX1) gene was proposed as a potential 'barcode'.

Some peculiar characters of the COI facilitate them for choosing as DNA barcode region. The mutation rate in mitochondrial genome is higher than the nuclear genome, particularly evolutionary rate of vertebrate mitochondrial gene roughly estimated as 1% sequence divergence per lineage per million years, maternally inherited with haploid transmission nature across generations etc.

Plant DNA Barcoding

COI gene is not appropriate for most species of plants because of a much slower rate of cytochrome c oxidase I gene evolution in higher plants than in animals. In plants, however, low substitution rates of mitochondrial DNA have led to the search for alternative barcoding regions. From initial investigations of plastid regions, 7 leading candidates have emerged. Four are portions of coding genes (matK, rbcL, rpoB, and rpoC1), and 3 are noncoding spacers (atpF-atpH, trnH-psbA, and psbK-psbI). Different research groups have proposed various combinations of these loci as their preferred plant barcodes, but no consensus has emerged.

Fungal DNA Barcoding

The ITS region is the most widely sequenced DNA region in molecular identification of fungi and has been recommended as the universal fungal barcode sequence. It has typically been most useful for molecular systematics at the species level, and even within species. The ITS region is flanked by the 18S rRNA gene at the 5'-end of the ITS-1 spacer and by the 28S rRNA gene at the 3' of the ITS-2 spacer. The highly conserved 18S, 5.8S, and 28S rRNA genes allow the design of universal primers to amplify the ITS-1, ITS-2, or the entire ITS region in the vast majority of fungi. Another major advantage of using ITS as a barcode is that each haploid genome typically contains multiple tandemly repeated copies of the ribosomal rRNA gene cluster (including ITS), making it possible to amplify this gene from small amounts of biological materials.

Bacterial DNA Barcoding

DNA barcode approaches enable the generation of complete phylogenetic hypotheses for entire communities of Bacteria by using universal primers allowing ecologists to tackle fundamental questions regarding to the processes triggering their distribution and assembly. The most commonly used barcode gene of bacterial and archaeal communities in studies is the small subunit ribosomal 16S rRNA gene.

Algae DNA Barcode

The efficiency of DNA barcoding in microalgae identification involves ideal gene markers and approaches employed, which however, is still under the way. The four genes, and their combined data rbcL?+?tufA?+?ITS?+?16S, rbcL?+?tufA and ITS?+?16S are used for DNA barcoding. Generally, three combined gene data showed a higher proportion of resolution success than the single gene. Character-based DNA barcoding together with other approaches based on multiple genes and their combined data could be more effective in microalgae diversity revelation.