Bicoid Morphogen Gradient

Diffusion–degradation model of positional information in Drosophila embryo

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Model: ∂c/∂t = D∇²c − λc + J(x). Steady state: c(x) = (J₀/λ)·exp(−x/λ_D) where λ_D = √(D/λ). Threshold crossings define gene expression boundaries (gap genes hb, kr, kni). Noise sensitivity ∝ 1/|dc/dx|.