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Silent substitutions in mammalian genomes and their evolutionary implications
G Bernardi1, D Mouchiroud, C Gautier
1Laboratoire de Génétique Moléculaire, Institut Jacques Monod, Paris, France.
Journal of Molecular Evolution
|December 1, 1993
Summary
Silent substitution rates in mammalian genes do not correlate with GC content. This finding challenges previous claims of mutation rate differences across mammalian genomes, suggesting sample size may explain discrepancies.
Area of Science:
- Genomics
- Molecular Evolution
- Bioinformatics
Background:
- Previous studies suggested variations in mutation rates and biases in mammalian genomes based on isochore composition.
- These variations were hypothesized to be linked to factors like nucleotide precursor pools and replication timing.
Purpose of the Study:
- To investigate the relationship between silent substitution frequencies and GC content in homologous mammalian genes.
- To re-evaluate claims of mutation rate differences and biases across mammalian genomic isochores.
Main Methods:
- Analysis of silent substitutions in pairwise comparisons of homologous genes across various mammalian species.
- Correlation analysis between substitution frequencies and GC levels of silent positions.
Main Results:
- Silent substitution frequencies, strongly correlated with substitutions per synonymous site, showed no average variation with GC levels of silent positions.
- This held true for gene pairs with similar and different GC compositions.
- Slightly lower frequencies at low GC values in specific pairs were attributed to small gene sample sizes.
Conclusions:
- The study contradicts claims of differing mutation rates and biases in mammalian third codon positions across isochores.
- Reported variations in mutation rates/biases are likely artifacts of small gene sample sizes and individual gene fluctuations.
- Cell cycle variations, replication timing, and repair efficiency differences do not appear to cause significant mutation rate or bias variations in mammals.