TABLE 1.

Substitution rate matrices for three separate influenza virus segments

Gene	Substitution rate (Pija) for:
	U	C	G	A
PB2	0.9977	0.0030	0.0009	0.0004
	0.0018	0.9969	0	0
	0.0002	0.0001	0.9961	0.0027
	0.0003	0	0.0030	0.9969
PB1	0.9988	0.0032	0.0008	0.0001
	0.0010	0.9968	0	0
	0.0001	0	0.9971	0.0012
	0.0001	0	0.0021	0.9987
PA	0.9979	0.0029	0.0003	0
	0.0018	0.9966	0	0
	0.0001	0	0.9973	0.0010
	0.0002	0.0005	0.0024	0.9990

^aP_ij is the number of substitutions per year, i is the nucleotide of the 1933 segment, and j is the nucleotide of the 1918 segment. The counting of nucleotides is done in the genomic sense (RNA−) and the order is U, C, G, A.