The tradeoff between nucleotide and amino acid compositions. Theoretical model. Black circles represent the genomes. The lower (green) and upper (red) limits for GCCB are calculated in the same way as in Figure 1a. The tradeoff describes the relation between the two components of GC depicted by an orange curve (with the coefficients a = 20.82, b = −16.28, c = −49.4, r = 0.255). The colored circles illustrate three pairs of genomes with the same GCNAT (45 percent – magenta, 51 – yellow, and 63 – blue) obtained by combining the GCCB and GCNCB in different proportions (see Additional file 1: Table S7 for details).