TOWARDS DETECTION OF ORTHOLOGUES IN SEQUENCE DATABASES

Motivation: Numerous homologous sequences from diverse species can be retrieved fr-om databases using programs such as BLAST. However; due t o multigene families, evolutionary relationship often cannot be easily determined and proper functional assignment becomes difficult. Thus, discrimination between orthologues and paralogues within BLAST output lists of homologous sequences becomes more and mole important. Result: We therefor-e developed a method that attempts to construct a reconci led tree fi-om a gene tl-ee of selected sequences and its correspondin g phylogenetic ti-ee of the species involved (species tree). An interf ace on the Web is developed to enable users to analyse the BLAST resul t. BLAST outputs are par sed and, for the selected sequences, multiple alignments are constructed either globally or for local regions. Boot strapped trees are returned and compared with the expected species tre e. In cases of discrepancies, gene duplications air assumed and a reco nciled tl ee is computed. The reconciled tree shows probable orthologu es and paralogues as predicted.