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.2008 Dec 10:3:50.
doi: 10.1186/1745-6150-3-50.

Are we degenerate tetraploids? More genomes, new facts

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Are we degenerate tetraploids? More genomes, new facts

Amir Ali Abbasi. Biol Direct..

Abstract

Background: Within the bilaterians, the appearance and evolution of vertebrates is accompanied by enormous changes in anatomical, morphological and developmental features. This evolution of increased complexity has been associated with two genome duplications (2R hypothesis) at the origin of vertebrates. However, in spite of extensive debate the validity of the 2R hypothesis remains controversial. The paucity of sequence data in early years of genomic era was an intrinsic obstacle in tracking the genome evolutionary history of chordates.

Hypothesis: In this article I review the 2R hypothesis by taking into account the recent availability of genomic sequence data for an expanding range of animals. I argue here that genetic architecture of lower metazoans and representatives of major vertebrate and invertebrate lineages provides no support for the hypothesis relating the origin of vertebrates with widespread gene or genome duplications.

Conclusion: It appears that much of the genomic complexity of modern vertebrates is very ancient likely predating the origin of chordates or even the Bilaterian-Nonbilaterian divergence. The origin and evolution of vertebrates is partly accompanied by an increase in gene number. However, neither can we take this subtle increase in gene number as an only causative factor for evolution of phenotypic complexity in modern vertebrates nor we can take it as a reflection of polyplodization events early in their history.

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Figures

Figure 1
Figure 1
A phylogeny of animals. Evolutionary relationship, numbers of genes and divergence times of selected animals whose genomes have been sequenced. Along with the increasing overall gene number, the occurrence of single HOX gene cluster in invertebrate genome and four or more clusters in vertebrate genome is taken as evidence for two rounds of whole genome duplication at the base of vertebrate lineage (2R hypothesis). The double headed arrow underneath shows the proposed time windows of genome amplification events. Features not drawn to scale.
Figure 2
Figure 2
Evolutionary history of Human HOX clusters and closely linked SP family members. Close physical linkage and congruency in the phylogenies of human SP gene family members and HOX clusters supports the view that vertebrate HOX gene clusters arose as a result of small scale gene duplication events involving chromosomal segments or gene clusters. 1d-3d, three rounds of segmental duplication. Features not drawn to scale.
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