The Brusselator model: ∂U/∂t = A − (B+1)U + U²V + Du∇²U, ∂V/∂t = BU − U²V + Dv∇²V. When B > 1 + A²(1 + Du/Dv·A²)^−1, the homogeneous state becomes Turing unstable, spontaneously breaking spatial symmetry into spots and stripes.