ROBUSTNESS TO DAMAGE OF BIOLOGICAL AND SYNTHETIC NETWORKS

We analyze the perturbation of the expression levels of thousandsof genes when one of them is knocked-out, by measuring avalanches, the numberof genes whose expression is affected in a knock-out experiment, and genesusceptibilities, which measure how often the expression of a given gene ismodified. Experimental data concerning the yeast S. cerevisiae are available.Knock-out is simulated, using random boolean network models of gene regulation,in several experiments, using different sets of boolean functions. The majorresults (when only canalizing functions are allowed) are that the distributionsof avalanches and susceptibilities are very similar in different syntheticnetworks, with very small variance, and that these two distributions closely resemblethe experimental ones (a result which is even more surprising since noparameter optimization has been performed). These results strongly suggestthat the distribution of avalanches and susceptibilities may be generic properties,common to many different genetic networks