title: Salmo salar and Esox lucius full-length cDNA sequences reveal changes in evolutionary pressures on a post-tetraploidization genome.
abstract: BACKGROUND
  Salmonids are one of the most intensely studied fish, in part due to their economic and environmental importance, and in part due to a recent whole genome duplication in the common ancestor of salmonids. This duplication greatly impacts species diversification, functional specialization, and adaptation. Extensive new genomic resources have recently become available for Atlantic salmon (Salmo salar), but documentation of allelic versus duplicate reference genes remains a major uncertainty in the complete characterization of its genome and its evolution.
  
  
  RESULTS
  From existing expressed sequence tag (EST) resources and three new full-length cDNA libraries, 9,057 reference quality full-length gene insert clones were identified for Atlantic salmon. A further 1,365 reference full-length clones were annotated from 29,221 northern pike (Esox lucius) ESTs. Pairwise dN/dS comparisons within each of 408 sets of duplicated salmon genes using northern pike as a diploid out-group show asymmetric relaxation of selection on salmon duplicates.
  
  
  CONCLUSIONS
  9,057 full-length reference genes were characterized in S. salar and can be used to identify alleles and gene family members. Comparisons of duplicated genes show that while purifying selection is the predominant force acting on both duplicates, consistent with retention of functionality in both copies, some relaxation of pressure on gene duplicates can be identified. In addition, there is evidence that evolution has acted asymmetrically on paralogs, allowing one of the pair to diverge at a faster rate.
authors.affiliation: Biology, Centre for Biomedical Research, University of Victoria, Victoria, British Columbia, V8W 3N5 Canada. bkoop@uvic.ca.
authors.forename: Jong S
authors.initials: JS
authors.lastname: Leong
authors.forename: Stuart G
authors.initials: SG
authors.lastname: Jantzen
authors.forename: Kristian R
authors.initials: KR
authors.lastname: von Schalburg
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Cooper
authors.forename: Amber M
authors.initials: AM
authors.lastname: Messmer
authors.forename: Nancy Y
authors.initials: NY
authors.lastname: Liao
authors.forename: Sarah
authors.initials: S
authors.lastname: Munro
authors.forename: Richard
authors.initials: R
authors.lastname: Moore
authors.forename: Robert A
authors.initials: RA
authors.lastname: Holt
authors.forename: Steven J M
authors.initials: SJ
authors.lastname: Jones
authors.forename: William S
authors.initials: WS
authors.lastname: Davidson
authors.forename: Ben F
authors.initials: BF
authors.lastname: Koop
mesh_terms: D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D020451:Contig Mapping; D018076:DNA, Complementary / Q000235:genetics*; D017859:Esocidae / Q000235:genetics*; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D020440:Gene Duplication; D020869:Gene Expression Profiling; D016678:Genome / Q000235:genetics*; D011123:Polyploidy; D020317:Salmo salar / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D018076:DNA, Complementary