An End to Endless Forms: Epistasis, Phenotype Distribution Bias, and Nonuniform Evolution
The r transcription factors bind to the promoters of k structural genes with affinities given by Dij. If the net activation to a promoter exceeds a threshold value (illustrated as a step function) the gene is expressed. The phenotype is described by the distribution of gene expression. This regulatory architecture corresponds to the single layered plan - See also our analysis of a generalized, multilayered, model.