Gene expression evolution after duplication
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Gene duplication is a mutational process that seeds genomes with new geneticmaterial. Ion channels comprise a large gene family that arose through gene duplicationsthat has played a substantial role in the evolution of novel traits across all of the domainsof life. For my dissertation, I investigated the evolutionary dynamics that allow geneduplicates to evolve novel functions. To do so, I focused on measuring and modeling theexpression evolution of voltage-gated sodium ion channel duplicates implicated in theconvergent evolution of electric organs in two families of electric fish.In chapter 1, I measured the expression stoichiometry of two sodium channelduplicates in electric fish species as well as non-electric relatives. I found that before amajor shift in expression from skeletal muscle and neofunctionalization in the musclederivedelectric organ, one of the duplicate genes was first down-regulated in theancestors of both electric lineages. In chapter 2, I introduce a new model of the dynamicsof duplicate genes co-evolving under dosage balance selection for their sharedexpression. I used the model to estimate the strength of selection on the duplicate genesfound in the electric fish lineages and to show that dosage balance selection impedes theevolution of novel function early after gene duplication but can later facilitate novelfunction evolution once a particular expression threshold is reached. In chapter 3 Iinvestigate the role a duplicate sodium channel played in the evolution of a novel electricorgan derived from motor neurons in a lineage of fish. In this lineage I show that aviskeletal-muscle-specific sodium channel duplicated and one of the duplicates gainedexpression in the spinal cord. In this tissue this channel exhibits sequence evolutionarypatterns consistent with it evolving to contribute to the unique electrophysiologicalattributes of the electric organ. This is the first observation of such a radical shift inexpression for a muscle-specific gene.