Figure 2. ΔGr64 mutants are severely deficient in the perception of most sugars Proboscis Extension Response (PER) of ΔGr64 mutants and isogenic control flies to 500mM (A) and 100mM (B) sugar solutions.

The genotype of ΔGr64 mutants is R1/+;R2/+;ΔGr64/ΔGr64 and that of the control flies is f03449/d06001. “Probability of Extension” represents the number of times flies from a given strain extended their proboscis when presented with a tastant, divided by the total number of times that the tastant was presented. For all data shown in Figure 2, each graph is the average of 4–15 experiments +/− SEM (3–11 flies per experiment, 20–105 flies total for each strain and tastant tested). Asterisks indicate a significant difference between the mutant and control strains, as determined by Student’s t-test (* indicates p<0.05, *** indicates p<0.0001). Glycerol was used as 10% or 2% solutions in water.

(C) The Gr5a gene is functional in R1/Y;R2/+;ΔGr64/ΔGr64 flies. Flies heterozygous for ΔGr64, but containing the same X chromosome (i.e. the same Gr5a) as the homozygous ΔGr64 flies, show normal and robust response to trehalose at both 100 mM and 500 mM concentrations.

(D) PER response of ΔGr64 mutant and control strains to various bitter tastants in the presence of 500mM fructose. The response to 500mM fructose alone is shown for comparison. There was no significant difference between mutants and controls for any of the bitter solutions by Student’s t-test.