Practice question

French flag model formulated by Lewis Wolpert explains how cells acquire positional information by interpreting concentration thresholds of a morphogen gradient from a localized source. Three outcome domains - blue high, white intermediate, red low - illustrate qualitative differences emerging from quantitative gradient readout via enhancer affinity. Model predicts identical competent cells adopt distinct fates depending on dose exposure. It underpins understanding of Drosophila Bicoid anterior gradient, vertebrate Shh limb and neural tube gradients and retinoic acid patterning, representing generic framework for concentration-dependent differentiation and pattern formation.