Examining the authenticity of "One-to-Four Model" in vertebrates through phylogenetic analysis of the proposed paralogon; Hsa4, Hsa5, Hsa8 and Hsa10

Abstract

Reconstruction of evolutionary history of all eukaryotic genomes (particularly vertebrates) has been an essential objective for evolutionary biologists. Long-term conservation of gene sequences and gene order are evidences of the heritage of each species and can be used to deduce distant ancestral genomes. About forty years ago, Susumo Ohno, suggested that vertebrate genomes expanded and evolved via various genome-wide duplications, within and across the clu·omosomes, creating gene duplicates. Chromosomal regions containing duplicate genes, termed as paralogons, are generally taken as remnants of two rounds of large scale duplications that are thought to have occurred in early vertebrate ancestry (the 2R hypothesis). This influential hypothesis has been a subject of heated debate over the past few decades. According to 2R hypothesis two rounds of genome duplication occurred in chordate evolution; one predating the Cambrian explosion, while the second occurred in early Devonian, after the radiation of actinopterygia and the sarcopterygian lineage. To test this hypothesis, phylogenetic analysis of multi gene families residing on human chromosomes HSA 4, 5, 8 and 10 was employed to estimate their evolutionary histories. Thus, phylogenetic trees of 10 gene families with tlu"ee and fourfold representation on respective chromosomes were conducted. Topology comparison approach was applied to identify genes that co-duplicated simultaneously during the vertebrate evolution. As a result two such distinct co-duplicated groups were identified. Genes of a particular co-duplicated group suggests that they might have duplicated concurrently with each other and exhibit identical evolutionary history while genes of two different co-duplicated groups do not share same evolutionary history and have not duplicated simultaneously. The results provided no solid evidence in support of whole genome duplication and revealed that the respective paralogon have been shaped via small scale duplication (segmental duplications) and rearrangement events of chromosomes (translocation events) that took place at different time points between invertebrate-vertebrate and teleost-tetrapod divergence.