title: Molecular evolution of genes in avian genomes.
abstract: BACKGROUND
  Obtaining a draft genome sequence of the zebra finch (Taeniopygia guttata), the second bird genome to be sequenced, provides the necessary resource for whole-genome comparative analysis of gene sequence evolution in a non-mammalian vertebrate lineage. To analyze basic molecular evolutionary processes during avian evolution, and to contrast these with the situation in mammals, we aligned the protein-coding sequences of 8,384 1:1 orthologs of chicken, zebra finch, a lizard and three mammalian species.
  
  
  RESULTS
  We found clear differences in the substitution rate at fourfold degenerate sites, being lowest in the ancestral bird lineage, intermediate in the chicken lineage and highest in the zebra finch lineage, possibly reflecting differences in generation time. We identified positively selected and/or rapidly evolving genes in avian lineages and found an over-representation of several functional classes, including anion transporter activity, calcium ion binding, cell adhesion and microtubule cytoskeleton.
  
  
  CONCLUSIONS
  Focusing specifically on genes of neurological interest and genes differentially expressed in the unique vocal control nuclei of the songbird brain, we find a number of positively selected genes, including synaptic receptors. We found no evidence that selection for beneficial alleles is more efficient in regions of high recombination; in fact, there was a weak yet significant negative correlation between omega and recombination rate, which is in the direction predicted by the Hill-Robertson effect if slightly deleterious mutations contribute to protein evolution. These findings set the stage for studies of functional genetics of avian genes.
authors.affiliation: Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, Uppsala, S-752 36, Sweden.
authors.forename: Kiwoong
authors.initials: K
authors.lastname: Nam
authors.forename: Carina
authors.initials: C
authors.lastname: Mugal
authors.forename: Benoit
authors.initials: B
authors.lastname: Nabholz
authors.forename: Holger
authors.initials: H
authors.lastname: Schielzeth
authors.forename: Jochen B W
authors.initials: JB
authors.lastname: Wolf
authors.forename: Niclas
authors.initials: N
authors.lastname: Backström
authors.forename: Axel
authors.initials: A
authors.lastname: Künstner
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Balakrishnan
authors.forename: Andreas
authors.initials: A
authors.lastname: Heger
authors.forename: Chris P
authors.initials: CP
authors.lastname: Ponting
authors.forename: David F
authors.initials: DF
authors.lastname: Clayton
authors.forename: Hans
authors.initials: H
authors.lastname: Ellegren
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000818:Animals; D001482:Base Composition / Q000235:genetics; D002645:Chickens / Q000235:genetics*; D002875:Chromosomes / Q000235:genetics; D019143:Evolution, Molecular; D046369:Finches / Q000235:genetics*; D016678:Genome / Q000235:genetics*; D009420:Nervous System / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D010802:Phylogeny; D011995:Recombination, Genetic; D012641:Selection, Genetic; D012689:Sequence Homology, Nucleic Acid