Evolution and characterization of the fatty acid-binding proteins (fabps) in Atlantic salmon (Salmo salar)

It is suggested that gene or genome duplication is the driving force in evolution that leads to speciation. Two models, the classical model and the duplication- degeneration-complementation (DDC) model, have been proposed on the fates of gene duplicates resulting from either a gene or a genome duplication event. The classical model suggests that one of the gene duplicates might result in loss of function (non- functionalization) or gain of a new function (neo-functionalization) depending on whether the accumulated mutations over the years are deleterious or beneficial to the organism. In the DDC model, it is proposed that each of the gene duplicates might accumulate different deleterious mutations in the regulatory region of the gene, such that these genes partition the ancestral gene function (sub-functionalization). Combinations of the phylogenetic analysis of many gene families support that salmonids have undergone two additional whole genome duplications compared to the mammals, one occurred in the common ancestors of teleosts and another happened in the common ancestor of salmonids approximately 25-120 million years ago. In this thesis, the evolution of the fatty acid-binding protein (fabp) family in fish and salmonids was examined. I have characterized eighteen unique fabp genes in Atlantic salmon. These include the seven fabp sub-families described previously in fish. Phylogenetic analyses and conservation of synteny support the two whole genome duplication events in the common ancestors of teleosts and salmonids and indicate when gene losses occurred. Genetic mapping of fabp gene duplicates to homeologous chromosomes in Atlantic salmon also support that they arose by the 4R genome duplication. I also searched for the signatures of neo-functionalization and sub-functionalization by calculating dN/dS ratios, examining the nature of amino acid substitutions and expression patterns, and suggested the fates of fabp gene duplicates in Atlantic salmon. Overall, the findings of this project provide insight into the evolutionary processes at play in salmonid genomes.