Fig 1.

Representation of a gene regulation network. Each gene (horizontal arrow) is regulated by the products of the other genes, via upstream enhancer elements (boxes). Strength and direction of regulation (depicted as different color saturation levels) are a function of both the regulatory element and the abundance of its corresponding gene product. Genotype is represented as the matrix, W, of regulatory interactions, and phenotype is the vector, Ŝ, of gene-product levels at equilibrium (see Methods).