Fig. 1. Schematic examples of the basic developmental mechanisms. Division of an heterogeneous egg: different parts of the egg bind different molecules (indicated by different shading) resulting in different blastomere cells. Asymmetric mitosis: molecules are differentially transported into different parts of a cell resulting in different daughter cells. Internal temporal dynamics coupled to mitosis: cells that have oscillating levels of molecules before their division can produce spatial patterns. Hierarchic induction: inducing cell (gray) affects neighboring cells but the induced cells (white) do not affect the production of the inducing signal. Emergent induction: inducing cell affects neighboring cells, which in turn signal back affecting the production of the inducing signal. Directed mitosis: consistently oriented mitotic spindles may direct tissue growth. Differential growth: cells dividing at a higher rate (gray) can alter tissue shape. Apoptosis: transformation of an established pattern into another can result from apoptosis affecting specific cells (gray). Migration: cells can migrate to a new location. Adhesion: a change in pattern can result if a set of cells have differential adhesion properties (strong adhesion among gray cells). Contraction: differential contraction of cells can cause buckling of a tissue. Matrix swelling, deposition, and loss: matrix swelling can cause budding.

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