title: Benchmarking ortholog identification methods using functional genomics data.
abstract: BACKGROUND
  The transfer of functional annotations from model organism proteins to human proteins is one of the main applications of comparative genomics. Various methods are used to analyze cross-species orthologous relationships according to an operational definition of orthology. Often the definition of orthology is incorrectly interpreted as a prediction of proteins that are functionally equivalent across species, while in fact it only defines the existence of a common ancestor for a gene in different species. However, it has been demonstrated that orthologs often reveal significant functional similarity. Therefore, the quality of the orthology prediction is an important factor in the transfer of functional annotations (and other related information). To identify protein pairs with the highest possible functional similarity, it is important to qualify ortholog identification methods.
  
  
  RESULTS
  To measure the similarity in function of proteins from different species we used functional genomics data, such as expression data and protein interaction data. We tested several of the most popular ortholog identification methods. In general, we observed a sensitivity/selectivity trade-off: the functional similarity scores per orthologous pair of sequences become higher when the number of proteins included in the ortholog groups decreases.
  
  
  CONCLUSIONS
  By combining the sensitivity and the selectivity into an overall score, we show that the InParanoid program is the best ortholog identification method in terms of identifying functionally equivalent proteins.
authors.affiliation: Centre for Molecular and Biomolecular Informatics, Radboud University Nijmegen, Toernooiveld 1, Nijmegen, 6500 GL, The Netherlands. T.Hulsen@cmbi.ru.nl
authors.forename: Tim
authors.initials: T
authors.lastname: Hulsen
authors.forename: Martijn A
authors.initials: MA
authors.lastname: Huynen
authors.forename: Jacob
authors.initials: J
authors.lastname: de Vlieg
authors.forename: Peter M A
authors.initials: PM
authors.lastname: Groenen
mesh_terms: D000465:Algorithms; D000818:Animals; D030541:Databases, Genetic; D019143:Evolution, Molecular; D015870:Gene Expression; D023061:Gene Order; D023281:Genomics / Q000379:methods*; D006801:Humans; D051379:Mice; D005810:Multigene Family; D025941:Protein Interaction Mapping; D011506:Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D012984:Software
chemical_list: D011506:Proteins