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Gene Duplication and Divergence02:37

Gene Duplication and Divergence

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The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was  generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are...
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Gene families consist of groups of genes proposed to have originated from a common ancestor. Typically these arise through events in which a gene or genes are mistakenly duplicated during cell division. Unlike their parent genes (which are subject to selection pressure to maintain function), these gene copies do not need to preserve their sequences and may evolve at a relatively faster rate.
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Genome Size and the Evolution of New Genes03:21

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While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.
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Eukaryotic Evolution01:24

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The endosymbiont theory is the most widely accepted theory of eukaryotic evolution; however, its progression is still somewhat debated. According to the nucleus-first hypothesis, the ancestral prokaryote first evolved a membrane to enclose DNA and form the nucleus. Conversely, the mitochondria-first hypothesis suggests that the nucleus was formed after endosymbiosis of mitochondria.
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The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes. 
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Origin Recognition Complex (ORC) Evolution Is Influenced by Global Gene Duplication/Loss Patterns in Eukaryotic

Eduard Ocaña-Pallarès1, Zaida Vergara2, Bénédicte Desvoyes2

  • 1Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Barcelona, Spain.

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The origin recognition complex (ORC) subunit evolution varies across eukaryotes, with parasites often having fewer subunits. ORC1

Keywords:
DNA replicationcentrioleeukaryotic evolutiongene lossorigin recognition complex (ORC)parasitism, whole genome duplication

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Area of Science:

  • Eukaryotic molecular biology
  • Evolutionary genomics
  • Cell biology

Background:

  • The origin recognition complex (ORC) is crucial for DNA replication initiation in eukaryotes.
  • Previous studies suggested ORC's universal presence across eukaryotes, but subunit composition varied.
  • Uncertainty existed regarding ancestral ORC diversification and specific subunit neofunctionalization, like ORC1's role in centriole homeostasis.

Purpose of the Study:

  • To reconstruct the evolutionary history and distribution of ORC subunits (ORC1-5/CDC6) across diverse eukaryotes.
  • To investigate the factors influencing ORC subunit number, such as genome duplication and streamlining.
  • To determine the evolutionary origin of ORC1's role in centriole homeostasis.

Main Methods:

  • Phylogenetic analysis of ORC subunits across a broad range of eukaryotic lineages.
  • Comparative genomics to assess subunit number variations in relation to genome size and lifestyle (free-living vs. parasitic).
  • Experimental manipulation of ORC1 levels in Chlamydomonas reinhardtii to study its effect on centriole biogenesis.

Main Results:

  • Identified previously undetected ORC subunits in various lineages, enabling parsimonious evolutionary reconstructions.
  • Observed a trend of increasing or decreasing ORC subunit numbers linked to genome duplication or streamlining.
  • Parasitic eukaryotes exhibit reduced ORC subunit counts, correlating with smaller genome sizes.
  • Reducing ORC1 levels in Chlamydomonas reinhardtii did not significantly alter the centriole-to-flagella/nuclei ratio.
  • The PACT region of ORC1 showed no significant conservation bias in centriole-bearing eukaryotes.

Conclusions:

  • Eukaryotic ORC subunit composition is dynamic, not universally conserved, and subject to genome size and lifestyle pressures.
  • The neofunctionalization of ORC1 for centriole homeostasis appears to be a recent evolutionary acquisition, not an ancestral eukaryotic trait.