Figure 2. The Modular Architecture of the cis-Regulatory Regions of Pleiotropic Genes Enables the Independent Evolution of Gene Expression in Different Body Parts.

(A) Expression of the yellow pigmentation gene of Drosophila is controlled by several different cis-regulatory elements (red circles). Differences in the activity of selected elements (wing and wing spot) underlie differences in pigment patterns between species (Figure based on [35].)

(B) Similarly, the expression of the Pitx1 gene of vertebrates is inferred to be controlled by multiple elements (red circles). In pelvic-reduced stickleback fish, Pitx1 expression is absent from the pelvic region. This is proposed to occur through of a selective loss of activity of the hindlimb regulatory element (cross through the red circle) (Figure based on [33].)