Genomes and their core- and pan-genomes. Number of genomes refer to completed genomes at NCBI  at the end of January 2009. Sample core, Median size and Sample pan are the observed quantities, while Mixture core, Chao pan and Mixture pan are estimated quantities. Components is the optimal choice of mixture components. The black bars under Coverage indicate pan-genome coverage, i.e. the current sample pan-genome size as a fraction of the estimated pan-genome size (Mixture pan).