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Rates of nucleotide substitution and mammalian nuclear gene evolution. Approximate and maximum-likelihood methods
J P Bielawski1, K A Dunn, Z Yang
1Department of Biology, University College London, London NW1 2HE, United Kingdom. j.bielawski@ucl.ac.uk
Genetics
|November 7, 2000
Summary
Accurate estimation of DNA substitution rates in mammals is crucial. Maximum-likelihood methods reveal GC content influences synonymous rates, unlike older approximate methods that showed biases.
Area of Science:
- Molecular Evolution
- Genomics
- Mammalian Genetics
Background:
- Synonymous and nonsynonymous substitution rates are key to understanding mammalian isochore evolution and selection efficacy.
- Previous studies often used approximate methods for estimating these rates, potentially yielding unreliable results due to unaddressed evolutionary complexities.
Purpose of the Study:
- To evaluate the impact of different estimation methods on DNA substitution rate analysis in mammals.
- To compare approximate methods with maximum-likelihood methods for accuracy in estimating synonymous and nonsynonymous substitution rates.
Main Methods:
- Analysis of 82 nuclear genes from Artiodactyla, Primates, and Rodentia.
- Comparison of approximate estimation methods versus maximum-likelihood methods.
- Inclusion of factors like transition/transversion rate bias and unequal codon usage in the analysis.
Main Results:
- Maximum-likelihood analysis showed synonymous substitution rates positively correlate with GC content at the third codon position, independent of nonsynonymous rates.
- Approximate methods incorrectly suggested independence from GC content and a positive correlation with nonsynonymous rates.
- Biases in approximate estimates were attributed to failure to account for transition/transversion bias and unequal codon usage.
Conclusions:
- Maximum-likelihood methods provide more reliable estimates of DNA substitution rates by accounting for key evolutionary parameters.
- Approximate methods can introduce substantial biases, potentially misinterpreting evolutionary dynamics in mammalian nuclear genes.
- GC content at synonymous sites is a significant factor influencing substitution rates, contrary to findings from less sophisticated methods.
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