Gene ontology categories associated with differentially expressed genes. A. The most significantly enriched GO categories (Fisher Exact Test, topGO elim algorithm , see Methods) at 2 h and 6 h are displayed in a heat map. The color intensity in each cell corresponds to the p-value (Fisher Exact Test) for the GO category that is enriched. The dendrograms were generated from a hierarchical clustering of GO Groups according to Resnik similarity . B. The most significantly enriched GO categories at 24 h were determined similarly.