(A) Measuring feeding preference with the FLIC assay. Flies are given a choice between a solution containing sucrose alone or sucrose mixed with a bitter compound. (B) Gr39a mutants have a reduced preference for all bitter compounds tested except DEN. Mann-Whitney test, n=9-12. (C) Oviposition preference paradigm. The oviposition preference is based on the number of eggs laid on each half of the plate. (D) Gr39a mutants have a reduced preference for all bitter compounds tested except DEN. Mann-Whitney test, n=9-10. (E) The physiological defect of Gr39a can be fully rescued by expression of the Gr39a.a splice form. One-way ANOVA followed by Tukey’s multiple comparison test, n=6-12. (F) Sample traces from the rescue experiment shown in E. (G) The feeding preference is rescued fully by a Gr39a.a transgene. Each tastant is tested at 10 mM except that COU was tested at 3 mM. One-way ANOVA followed by Tukey’s multiple comparison test, n=10-18 (H) The oviposition preference is rescued fully by a Gr39a.a transgene. CAF, THE, and TPH were tested at 100 mM; UMB and COU were tested at 10 mM and 3 mM respectively. One-way ANOVA followed by Tukey’s multiple comparison test, n = 10. In (E-H), values indicated with different letters are significantly different. The key shown for (E) applies to (G,H). See also Figure S3.