title: Reduced efficacy of selection in regions of the Drosophila genome that lack crossing over.
abstract: BACKGROUND
  The recombinational environment is predicted to influence patterns of protein sequence evolution through the effects of Hill-Robertson interference among linked sites subject to selection. In freely recombining regions of the genome, selection should more effectively incorporate new beneficial mutations, and eliminate deleterious ones, than in regions with low rates of genetic recombination.
  
  
  RESULTS
  We examined the effects of recombinational environment on patterns of evolution using a genome-wide comparison of Drosophila melanogaster and D. yakuba. In regions of the genome with no crossing over, we find elevated divergence at nonsynonymous sites and in long introns, a virtual absence of codon usage bias, and an increase in gene length. However, we find little evidence for differences in patterns of evolution between regions with high, intermediate, and low crossover frequencies. In addition, genes on the fourth chromosome exhibit more extreme deviations from regions with crossing over than do other, no crossover genes outside the fourth chromosome.
  
  
  CONCLUSIONS
  All of the patterns observed are consistent with a severe reduction in the efficacy of selection in the absence of crossing over, resulting in the accumulation of deleterious mutations in these regions. Our results also suggest that even a very low frequency of crossing over may be enough to maintain the efficacy of selection.
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, EH9 3JT, UK. p.haddrill@ed.ac.uk
authors.forename: Penelope R
authors.initials: PR
authors.lastname: Haddrill
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Halligan
authors.forename: Dimitris
authors.initials: D
authors.lastname: Tomaras
authors.forename: Brian
authors.initials: B
authors.lastname: Charlesworth
mesh_terms: D000818:Animals; D001483:Base Sequence; D003062:Codon / Q000235:genetics; D019295:Computational Biology; D003434:Crossing Over, Genetic; D004330:Drosophila / Q000235:genetics*; D019143:Evolution, Molecular; D016678:Genome / Q000235:genetics*; D007438:Introns / Q000235:genetics; D016013:Likelihood Functions; D012641:Selection, Genetic; D016415:Sequence Alignment; D013045:Species Specificity
chemical_list: D003062:Codon