The distributions of GC difference within genomes. The histograms show the distribution of GC difference, D
, (Equation (1) in the Methods section) for eight different microbial genomes. The blue curves are empirical density estimates, while the red curves are Gaussian densities using based on the same means and standard deviations as the empirical estimates. The upper panels show the statistical distributions for four AT rich genomes, while the lower panels show the distributions for four GC rich genomes.