Before revision: Based on data on gene expression profiles from microarrays for E. Coli and tumor tissues, I show the existence of heavy tails in the gene expression distribution functions, related to a set of strongly over- and under-expressed genes .
After revision: Based on data on gene expression profiles from microarrays for E. Coli and tumor tissues, I show that the evolution for thousands of generations leads to a set of strongly over- and under-expressed genes .