On the role of sparseness in the evolution of modularity in gene regulatory networks
Fig 3
Modularity evolves after selection for an additional gene activity phenotype.
(A) Target GAPs I and II. White and black squares represent active and inactive genes, respectively. Genes 1-5 are grouped in set and genes 6-10 are grouped in set
. Note that genes in set
have the same activity state in both target GAPs. In contrast, genes in set
have a different activity state in both target GAPs. Networks evolve in a first stage under selection to produce target GAP I. In a second stage, selection favours networks that produce target GAPs I and II from distinct initial system states, that may occur, for example, in cells in different parts of an organism. (B)
increases after selection for an additional gene activity phenotype. Each dot represents an independently evolving population. The horizontal axis indicates the
score for a network with the highest fitness before starting selection for the two GAPs. The vertical axis denotes the same score but for a network after selection for both GAPs. The solid diagonal is the identity line. (C) After selection for GAP I alone, interactions between any pair of genes occur with similar frequency. Grayscale indicates the fraction of independently evolved networks that have a certain source-target regulatory interaction. (D) After selection for both target GAPs I and II interactions occur mainly either between genes in set
or between genes in set
.