Correlation between the branch lengths in different phylogenetic partitions. Linear regression where the bA branch length (y-axis) is plotted against the sum of bB + bC branch lengths (x-axis) for all orthologous protein sets of each species group. (a) Chlamydiaceae species group including C. pneumoniae, C. muridarum and C. trachomatis. (b) Pyrococcus species group including P. furiosus, P. abyssi and P. horikoshii. (c) Human-mouse-rat species group including H. sapiens, M. musculus and R. norvegicus. The equation for the linear regression trend line (y = mx + b), the correlation coefficient (r) and the level of significance for the correlation (P) are shown on each plot. The linear regression trend line is shown in bold black and the upper and lower limits, corresponding to an expectation value of 0.05, are shown in light gray. For each plot, only 0.05 points are expected to fall outside of these limits by chance. All values are shown as diamonds and the values outside the upper and lower limits that represent functionally diversified orthologous protein sets are indicated by larger squares.