Distribution of repeat sequences between pneumococcal genomes. a) For each of the three families of small, interspersed repeat, and for IS elements, orthologous insertion events were defined between chromosomes (see Methods) and scored for presence or absence in the 13 complete pneumococcal clinical isolate chromosomes. The bar chart shows the proportion of insertions of each repeat element shared by a given number of pneumococcal sequences, ranging from insertions present in a single chromosome to those conserved among all strains. b) Variation in the length of BOX elements. For each BOX element identified in the chromosome sequences, the mean, minimum and maximum sizes of orthologous inserts in different strains was calculated. The graph shows the mean length plotted against the range in size, with the dotted bars showing the span of sizes detected.