FIGURE 2.

(A) Extrinsic cause of heterogeneity. Two isogenic cells are fed dissimilar signals because of environmental noise, leading to different responses. (B–E) Cell–cell heterogeneity because of intracellular noise. (B) Small number of Transcription Factor molecules (circles) take widely different time to search for the promoter site (red) on DNA (blue line). (C) Cellular processes such as transcription occur with exponentially distributed periods of bursts of activity. (D) Cell–cell variation because of unequal partitioning at cell division, (E) Feedback in cellular networks leads to all (black) or none (white) states in cellular physiology.