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. Author manuscript; available in PMC: 2012 Mar 18.
Published in final edited form as: Cell. 2011 Mar 18;144(6):970–985. doi: 10.1016/j.cell.2011.02.017

Fig. 2. Functional evolutionary consequences of cis-regulatory mutations depend on their location in GRN architecture.

Fig. 2

A GRN circuit encoding the control system of a differentiation gene battery (bottom tiers) activated in response to a signal (S) from adjacent cells (top tier); linkages shown in gray and genes in black. The double arrow indicates signal reception and transduction causing gene expression in the recipient cells. Note that the middle tier of circuitry consists of a dynamic feedback stabilization subcircuit. The numbered red “x” symbols denote mutational changes in the cis-regulatory modules controlling expression of these genes, keyed by number to the functional consequences listed in the box below. Loss of function mutations (1 and 2) are indicated in green, and co-optive gain of function mutations (3 and 4) resulting in expression of the affected gene in a new domain, as in Fig.1A, are indicated in gray (modified from Erwin and Davidson, 2009).