Thesis advisor: John Wing / Thesis advisor: Stephen Wicks / Molecular biology and genetics, single nucleotide polymorphism genetic mapping, phenotypic assays including behavioral assessment, and fluorescent microscopy of GFP-tagged proteins were used to study ciliary defects in the nematode Caenorhabditis elegans. Mammalian cilia are multifunctional. Some of the physiological roles in which they are involved include sensing developmental signaling molecules and ligands as well as creating flows of mucus and cerebrospinal fluid that function as flow meters and mechanosensors. Due to the multifunctional nature of cilia, it is not surprising that many human diseases can be caused by ciliary defects. Bardet-Biedl Syndrome is a rare genetic ciliopathy characterized by retinal degeneration, polydactyly, obesity, cystic kidneys, mental retardation, and many other ailments. We have identified osm- 12/bbs-7 to be a C. elegans homologue of human BBS7, a gene known to cause Bardet-Biedl Syndrome when mutated. With the help of Michel Leroux’s group, I showed the BBS-7 protein to be localized to the base of cilia and to undergo intraflagellar transport along the ciliary axoneme. Our findings suggest that BBS- 7 plays a role in the assembly and/or functioning of the IFT complex. I also performed a mutagenesis and phenotypic screen for animals defective in the uptake of DiI into a subset of their ciliated neurons in order to identify new components involved in ciliogenesis and IFT. I describe an extended bulked segregant analysis (BSA) mapping methodology, which can save time and resources by filtering out alleles of previously known genes without performing time-consuming interval mapping. In addition, I identified one of the 11 dyefilling defective alleles from the screen to be a novel allele of dyf-3, which encodes a protein required for sensory cilia formation. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.