Schematic illustration of how population measurements, such as Western blotting (A) cannot distinguish between graded (B) versus discrete responses (C). Sample cell population show gradual increase in marker expression as indicated by increasing hue (B) or switch-like response with cells either expressing or not expressing a marker upon stimulation (C). Flow cytometry histograms reveal the difference: a graded response would appear as one peak gradually shifting in intensity (B) whereas a bistable response would lead to two distinct peaks that alternatively grow or wane (C). "Stimulus" indicates duration of stimulation or concentration of stimulant.
Chang et al. BMC Cell Biology 2006 7:11 doi:10.1186/1471-2121-7-11