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Related Experiment Videos

Are evolutionary rates really variable?

J H Gillespie, C H Langley

    Journal of Molecular Evolution
    |June 8, 1979
    PubMed
    Summary

    The rate of nucleotide substitutions in proteins may not be temporally heterogeneous. A homogeneous but non-Poisson process, with a specific coefficient of variation, aligns with observed protein evolution data.

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    Area of Science:

    • Molecular Evolution
    • Population Genetics
    • Bioinformatics

    Background:

    • Previous studies suggested temporal heterogeneity in nucleotide substitution rates based on protein data.
    • Langley and Fitch's work indicated deviations from a constant-rate Poisson process.
    • This challenges simple models of molecular evolution.

    Purpose of the Study:

    • To re-evaluate the interpretation of protein nucleotide substitution patterns.
    • To explore alternative models compatible with existing data.
    • To investigate the expected patterns from neutral phylogenies.

    Main Methods:

    • Statistical analysis of nucleotide substitution patterns.
    • Modeling of temporally homogeneous, non-Poisson processes.
    • Theoretical analysis of neutral phylogenetic samples.

    Main Results:

    • A temporally homogeneous, non-Poisson process with a coefficient of variation around 1.63 fits the observed data.
    • Theoretical neutral phylogenies deviate from a Poisson process in a similar direction to empirical data.
    • The observed patterns are not exclusively indicative of rate heterogeneity.

    Conclusions:

    • The assumption of a constant-rate Poisson process may be inappropriate for molecular evolution.
    • Temporal homogeneity is compatible with observed substitution patterns under a non-Poisson model.
    • Deviations from Poisson processes are expected in neutral phylogenies, supporting alternative evolutionary models.

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