Morphogen Gradients

Lewis Wolpert (1969): morphogen gradients encode positional information. Cells read local concentration and differentiate into distinct fates when crossing thresholds. The steady-state profile follows c(x) = c₀·exp(−x/λ) where λ = √(D/k) is the characteristic length. The precision of boundary specification depends on the gradient slope and noise level — the "French flag" model. Modern example: Bicoid gradient in Drosophila.