Practice question

Lewis Wolpert's French flag model proposed that positional information is encoded by a diffusible morphogen gradient. Cells detect local ligand concentration through surface receptors and intracellular transducers, converting continuous gradient into discrete thresholds. Low, intermediate and high doses activate distinct enhancers and transcription factors, producing three broad fate domains resembling a tricolour flag. Thus fate depends not on receptor number, mitotic rate or linear distance but on quantitative interpretation of morphogen exposure during patterning of limb buds, neural tube and Drosophila imaginal discs and vertebrate axis.