Codon bias evolution in Drosophila. Population genetics of mutation-selection drift

Area of Science:

• Genetics
• Evolutionary Biology
• Molecular Biology

Background:

• Synonymous codon usage bias is common in genomes, but the roles of mutation and natural selection are debated.
• The 'major codon preference' model suggests a balance between mutation pressure, genetic drift, and weak selection for translationally efficient codons.
• Population genetics offers models to differentiate mutational bias from selection-driven codon bias.

Purpose of the Study:

• To investigate the dynamics of preferred and unpreferred silent mutations in Drosophila species.
• To distinguish between mutational and selection-based models of codon bias maintenance.
• To assess the relative contributions of natural selection and genetic drift to codon bias.

Main Methods:

• Utilized an extension of current statistical methods.
• Analyzed within and between-species dynamics of silent mutations in Drosophila simulans.
• Compared codon bias patterns in Drosophila simulans and Drosophila melanogaster.

Main Results:

• In Drosophila simulans, codon bias is maintained by roughly equal forces of natural selection and genetic drift.
• In Drosophila melanogaster, a decrease in effective population size (N(e)s) correlated with a genome-wide reduction in codon bias.
• Identified two fitness classes of synonymous DNA changes: 'preferred' and 'unpreferred' mutations.

Conclusions:

• Codon bias is influenced by the interplay of mutation, selection, and genetic drift.
• Effective population size plays a critical role in the maintenance and reduction of codon bias.
• The findings support a model where selection acts on synonymous codon usage, modulated by population genetics factors.