Chaser (Csr) was uncovered in a gamma mutagenesis screen to identify genes that modify the larval foraging behavior of sitters to rovers. Rover larvae have significantly longer path lengths than sitters while foraging on a yeast and water paste. This difference is influenced by one major gene, foraging (for), which has two naturally occurring alleles, forR (rover) and fors (sitter). In a mutagenesis screen for modifiers of for, we identified three lines with viable mutations on chromosome 3 that alter foraging behavior. Each of these mutations increased larval path lengths in fors/fors larvae in a dominant fashion, and were not separable by recombination. These mutations are therefore probably allelic and define a new gene that we have called Csr. Csr was genetically localized using the lethal-tagging technique. This technique resulted in seven lines with a significant decrease in larval path-length and recessive lethal mutations on chromosome 3. We refer to these as reverted Csr (Csrrv) lines. Deficiencies that uncovered cytologically visible chromosome rearrangements in three of the seven reverted lines were used in a complementation analysis. In this way we mapped the lethal mutations in the Csrrv lines to cytological region 95F7-96A1 on the right arm of chromosome 3.
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