Fig. 4. Fluctuations of the GFP-Dpp gradient in the absence of endogenous Dpp for 30 gradients. Genotype: dpp^d8/dpp^d12; dppGal4/UAS-GFP-Dpp. (A,B) GFP-Dpp gradient (A, green) and PMad immunostaining (B, red) to identify the source boundary (dotted line), located at x=0 in C-F. Disk size L (yellow line). The white box indicates the square which is scanned to perform the measurement. Scale bars: 10 µm. Posterior, right. (C) GFP-fluorescence intensity (FI) c^Dpp(x) in the white squares shown in A as a function of the distance to the source. Two profiles (in the dorsal and ventral compartments) were recorded per disk. (D) Mean FI c^-Dpp(x) at each position (yellow line) with error bars (black region surrounding the yellow line) showing the standard deviation. Red line, fit of the function C₀exp(-x/^Dpp) to the mean profile. The uncertainty of the FI leads to an uncertainty of the position where this FI is present. (E) Standard deviation of the FI. (F) Relative uncertainty of the FI for the ensemble of gradients. Note the qualitative similarity to Fig. 2E. Insets in C-F show corresponding results for the normalized Dpp profiles. Green horizontal bars in C-F, 5 cell diameters (13 µm).