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Classification of organisms on the basis of morphology and fossil records is not accurate therefore protein barcoding using Cytochrome C oxidase subunit 1 (COX1) is used to identify and classify different organisms. COX1 due to its presence in all the animals was selected in this study for phylogeny reconstruction. Classes of subphylum vertebrata including Amphibia, Reptillia, Chondrichthyes, Osteichthyes and Aves were examined. Total 60 homologous sequences were analyzed, ten from each mentioned class and one sequence was added as an out group. A maximum-likelihood (ML) tree was reconstructed which depicted many important results including evolutionary relationships among these classes. The reconstructed phylogenetic tree was clustered into five unique clades. The early divergence of monophyletic group of mammals was revealed by a separate branch from other classes of subphylum vertebrata. Homo sapiens were revealed to be closely related to common chimpanzee. The minimum mean distance was found among individual organisms of Aves group and maximum mean distance was found among organisms of Reptilia which revealed that Reptiles belong to a class of most diverged species. Similarly, the minimum average evolutionary divergence was exhibited between groups of amphibians and reptiles and maximum was found between groups of mammals and chondrichthyes. Cytochrome oxidase subunit 1 is a powerful system in reconstruction of phylogenetic relationships among various species.
Keywords: Cytochrome oxidase subunit 1; maximum-likelihood; mitochondrial DNA; phylogeny; vertebrata