![]() Since then, international initiatives have been launched across hundreds of countries to evaluate the world’s bio-diversities using this new taxonomic tool, and more than 321 K species, covering animals, plants, fungi and others, have been barcoded so far (Jeanson et al. Nevertheless, the novel concept of DNA barcode relying upon nucleotide divergence was not formally proposed and established for species diagnosis until 2003 by Hebert PD et al. The advent of techniques for gene isolation, cloning and Sanger sequencing in the second half of last century allows the term “DNA barcode” to be first used in 1993 when length information of tandemly repeated DNA sequences from hypervariable alleles was barcoded to discriminate isolates of Plasmodium falciparum (Arnot et al. Before that, 250 years have been spent to catalogue about 1.2 million species by traditional taxonomic approaches through manual characterizations incorporating morphological features, which apparently is challenging and unrealistic when it is forecasted that around 7.52 million terrestrial species and 2.01 million species in the ocean still await description (Leray and Knowlton 2016 Scheffers et al. In fact, the history of genetic sequences applied in taxonomy research can be traced back to 1969 when Bicknell and Douglas found that the arrangement of species in yeast dependent on ribosomal RNA homologies in most cases agreed with the established taxonomic groupings via traditional measures (Bicknell and Douglas 1970). Here we intend to give an overview of the characteristics and features of these barcode markers and major reference libraries existing for barcoding the planet’s life, as well as to address the limitations and opportunities of DNA barcodes to an increasingly broader community of science and society. Consequently, global DNA barcoding campaigns have resulted in the formation of many online workbenches and databases, such as BOLD system, as barcode references, and facilitated the development of mini-barcodes and metabarcoding strategies as important extensions of barcode techniques. Other standardized regions meeting barcoding criteria then are also evolving as DNA barcodes for fast, reliable and inexpensive assessment of species composition across all forms of life, including animals, plants, fungi, bacteria and other microorganisms. ![]() The modern concept of DNA-based barcoding for cataloguing biodiversity was proposed in 2003 by first adopting an approximately 600 bp fragment of the mitochondrial COI gene to compare via nucleotide alignments with known sequences from specimens previously identified by taxonomists.
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