Fig. 3

Magnitude of significant determining factors of codon usage bias in polymerase genes of EIVs. ENc-plot: the red dotted line represents the expected curve of positions of strains when the codon usage was only determined by the GC3s composition. Neutrality plot: the red dotted line is the linear regression of GC12 against GC3. PR2 bias plot: AU-bias [A3/(A3 + U3)] at the third codon position of the four-codon amino acids of entire genes were plotted against the GC-bias [G3/(G3 + C3)] and the centre of the plot represents no bias between the influence of the mutation pressure and natural selection