Understanding the genetic architecture of complex traits requires identification of the underlying genes and characterization of gene-by-gene and genotype by environment interactions (GEI). Behaviors that mediate interactions between organisms and their environment are complex traits that are especially sensitive to environmental conditions. Drosophila melanogaster presents an opportunity to systematically dissect epistasis and GEI, since large numbers of genetically identical individuals can be reared under defined environmental conditions. The olfactory system of Drosophila and its behavioral response to odorants have been well characterized. Previous studies on olfactory behavior have shown that the genetic architecture of this model behavior depends on epistatic networks of pleiotropic genes. I have used P-element mutagenesis in a co-isogenic background to identify genes that contribute to olfactory behavior. I have demonstrated that the effects of the transposon insertions are often dependent on developmental stage and that hypomorphic mutations in developmental genes can elicit profound adult behavioral deficits. I also assessed epistasis among these genes by constructing all possible double heterozygotes and measuring avoidance responses at two odorant concentrations. I observed enhancer and suppressor effects among subsets of these genes, and surprisingly, these epistatic interactions shifted with changes in the concentration of the olfactory stimulus. I then assessed variation in olfactory behavior in a population of 41 wild-derived inbred lines and asked to what extent different larval rearing environments would influence adult olfactory behavior and whether GEI is a minor or major contributing source of phenotypic variation. My results show that about 50% of phenotypic variation in adult olfactory behavior is attributable to GEI. In contrast, transcriptional analysis revealed that only 20 genes show GEI at the level of gene expression (FDR<0.05), some of which are associated with physiological responses to environmental chemicals. Quantitative complementation tests with piggyBac-tagged mutants for two of these genes (CG9664 and Transferrin 1) demonstrate that genes that show transcriptional GEI are candidate genes for olfactory behavior, and that GEI at the level of gene expression is correlated with GEI at the level of phenotype.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-06032008-131124 |
| Date | 08 July 2008 |
| Creators | Sambandan, Deepa |
| Contributors | Patricia A. Estes, Christina M. Grozinger, Trudy F.C. Mackay, Robert R. H. Anholt |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-06032008-131124/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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