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. 2013 Sep;35(9):829-37.
doi: 10.1002/bies.201300037. Epub 2013 Jun 25.

Genome Reduction as the Dominant Mode of Evolution

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Free PMC article

Genome Reduction as the Dominant Mode of Evolution

Yuri I Wolf et al. Bioessays. .
Free PMC article

Abstract

A common belief is that evolution generally proceeds towards greater complexity at both the organismal and the genomic level, numerous examples of reductive evolution of parasites and symbionts notwithstanding. However, recent evolutionary reconstructions challenge this notion. Two notable examples are the reconstruction of the complex archaeal ancestor and the intron-rich ancestor of eukaryotes. In both cases, evolution in most of the lineages was apparently dominated by extensive loss of genes and introns, respectively. These and many other cases of reductive evolution are consistent with a general model composed of two distinct evolutionary phases: the short, explosive, innovation phase that leads to an abrupt increase in genome complexity, followed by a much longer reductive phase, which encompasses either a neutral ratchet of genetic material loss or adaptive genome streamlining. Quantitatively, the evolution of genomes appears to be dominated by reduction and simplification, punctuated by episodes of complexification.

Keywords: ancestral reconstruction; archaea; genome complexification; genome reduction; horizontal gene transfer; orthologs.

Figures

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Figure 1
Figure 1
Reconstruction of the evolution of the archaea.The color code indicates the number of genes that belongs to clusters of archaeal orthologous genes (arCOGs) in the extant genomes and the reconstructed number of arCOGs in the ancestral forms . The figure is modified from .
Figure 2
Figure 2
The biphasic model of punctuated evolution of genomes. Top: Periods of compressed cladogenesis punctuating long phases of quasi-stasis in the history of a particular lineage. Bottom: Complexity profile. The vertical axis implies the biological complexity of genomes that can be expressed as the number of sites or genes that are subject to selection. The green background indicates the complexification phase and the red background indicates the reduction phase.The dashed lines indicate the super-exponential growth rate in the complexification phase.

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