title: The expansion of amino-acid repeats is not associated to adaptive evolution in mammalian genes.
abstract: BACKGROUND
  The expansion of amino acid repeats is determined by a high mutation rate and can be increased or limited by selection. It has been suggested that recent expansions could be associated with the potential of adaptation to new environments. In this work, we quantify the strength of this association, as well as the contribution of potential confounding factors.
  
  
  RESULTS
  Mammalian positively selected genes have accumulated more recent amino acid repeats than other mammalian genes. However, we found little support for an accelerated evolutionary rate as the main driver for the expansion of amino acid repeats. The most significant predictors of amino acid repeats are gene function and GC content. There is no correlation with expression level.
  
  
  CONCLUSIONS
  Our analyses show that amino acid repeat expansions are causally independent from protein adaptive evolution in mammalian genomes. Relaxed purifying selection or positive selection do not associate with more or more recent amino acid repeats. Their occurrence is slightly favoured by the sequence context but mainly determined by the molecular function of the gene.
authors.affiliation: Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland. Fernando.CruzRodriguez@unil.ch
authors.forename: Fernando
authors.initials: F
authors.lastname: Cruz
authors.forename: Julien
authors.initials: J
authors.lastname: Roux
authors.forename: Marc
authors.initials: M
authors.lastname: Robinson-Rechavi
mesh_terms: D000818:Animals; D001482:Base Composition; D055028:Comparative Genomic Hybridization; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D016678:Genome; D008322:Mammals / Q000235:genetics*; D008957:Models, Genetic; D020449:Repetitive Sequences, Amino Acid / Q000235:genetics*; D012641:Selection, Genetic; D016415:Sequence Alignment