Figure 6.

G+C content over the three codon positions. Chi-square values of G+C content over the three codon positions for genes assigned to lineages of increasing depth in the reference tree topology. Chi-square values were calculated using the expected G+C codon-position values derived from the three linear equations provided by Lawrence and Ochman [3] (see equations 13, 14 and 15 therein). At the right-bottom side of the figure, the correlation between genomic G+C content and G+C content at the three codon positions based on the data provided by Muto and Osawa [50] is provided. Genes that are still under the amelioration process are expected to deviate from those expected values. The expected G+C content for each codon position in the Salmonella lineage is highlighted in red.