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GC-biased segregation of noncoding polymorphisms in Drosophila
Nicolas Galtier1, Eric Bazin, Nicolas Bierne
1UMR 5171, "Génome, Populations, Interactions, Adaptation," CNRS, Université Montpellier 2, IFREMER, 34095 Montpellier, France. galtier@univ-montp2.fr
Genetics
|September 15, 2005
Summary
GC-biased gene conversion influences Drosophila DNA base composition evolution. Analysis of noncoding DNA reveals asymmetric mutation patterns, suggesting biased transmission rather than just mutation bias.
Area of Science:
- Evolutionary biology
- Population genetics
- Molecular evolution
Background:
- Base composition evolution in Drosophila is often studied via coding sequences.
- Third codon position GC content is affected by mutation bias and selection for codon usage.
- Noncoding DNA offers a way to study evolution without selection for codon usage.
Purpose of the Study:
- To disentangle neutral forces and selection in Drosophila base composition evolution.
- To analyze noncoding DNA sequence polymorphism in D. melanogaster and D. simulans.
- To investigate the role of biased transmission and GC-biased gene conversion.
Main Methods:
- Gathering large datasets of noncoding DNA sequence polymorphism from public databases.
- Performing allele frequency analyses on AT vs. GC polymorphisms.
- Fitting population genetics models to allele frequency spectra.
Main Results:
- An asymmetric pattern of AT vs. GC noncoding polymorphisms was observed.
- AT --> GC mutations were less numerous and segregated at higher frequencies than GC --> AT mutations.
- Population genetics models favored the hypothesis of biased transmission, specifically GC-biased gene conversion.
Conclusions:
- Noncoding DNA polymorphism analysis suggests nonstationary base composition evolution in Drosophila.
- GC-biased gene conversion likely influences base composition evolution.
- This mechanism explains the correlation between intron and exon GC content.