suppose the activity of the switch depends on the concentration of the protein, and the protein can be layered in a gradient across the body of an organism, with a high concentration at one end and a low concentration at the other. This protein might flick on all twelve of its targets in one part of an organism, eight in another segment, and only three in yet another. Each combination of target genes (twelve, eight, and three) might then intersect with yet other protein gradients, and activate and repress yet other genes.
