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Related Experiment Videos

Molecular clock or erratic evolution? A tale of two genes

F J Ayala1, E Barrio, J Kwiatowski

  • 1Department of Ecology and Evolutionary Biology, University of California, Irvine 92697, USA.

Proceedings of the National Academy of Sciences of the United States of America
|October 15, 1996
PubMed
Summary

Evolutionary rates of glycerol-3-phosphate dehydrogenase (Gpdh) and Cu,Zn superoxide dismutase (Sod) were analyzed. Gpdh evolution accelerated with divergence, unlike Sod, challenging molecular clock models.

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Area of Science:

  • Evolutionary biology
  • Molecular evolution
  • Biochemistry

Background:

  • The molecular clock hypothesis posits a constant rate of molecular evolution.
  • Understanding protein evolution rates is crucial for phylogenetic analysis.
  • Glycerol-3-phosphate dehydrogenase (Gpdh) and Cu,Zn superoxide dismutase (Sod) are key enzymes with different functional constraints.

Purpose of the Study:

  • To investigate the evolutionary rates of Gpdh and Sod across different taxonomic divergences.
  • To assess the consistency of these rates with the molecular clock hypothesis and the covarion model.

Main Methods:

  • Comparative sequence analysis of Gpdh and Sod across various species, including Drosophila, Chymomyza, Ceratitis capitata, mammals, and different animal phyla.
  • Calculation of amino acid replacement rates per site per year.

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Main Results:

  • Gpdh evolutionary rates increased significantly with greater species divergence (from 1x10^-10 to 5x10^-10/site/year).
  • Sod evolutionary rates showed a decrease with increased divergence (from 17x10^-10 to 3x10^-10/site/year), potentially explained by the covarion model.
  • The observed increase in Gpdh rates contradicts simple molecular clock models.

Conclusions:

  • The evolution of Gpdh and Sod exhibit distinct patterns inconsistent with a universal molecular clock.
  • The covarion hypothesis may explain Sod's rate variation but not Gpdh's acceleration.
  • Further models are needed to account for the complex evolutionary dynamics of Gpdh.