Characteristics of within-group SDs found in each gene of mice fed with different diets. A: Between group comparisons in Agilent chip data for standard (Cy-5) and high-calorie (Cy-3) diets ; B: Affymetrix GeneChip data for the stearoyl-CoA desaturase 1 mutant (Group 2) and wild type (Group 4) . Black: real data; green: virtual data (Methods). C: Dependence of observed SDs to signal intensities. Standard deviations of the Cy-5 channel of panel A, the standard diet group, plotted against the ranks of mean signal intensities in ascending order. Only 1,000 of randomly selected data are presented in each panel to avoid graphical saturations.