Table 4. Codon position-wise analysis of transition preference in nucleotide substitutions during evolution of poliovirus VP1 coding sequences in different contexts.

			Sequence set
			Slovakian VDPV2	Andean WPV1	Finland WPV3	Nigerian cVDPV
No. of strains			102	31	21	361
Test category		Codon position
Transition/transversion bias		1,2,3	5.6	10.6	7.3	9.3
		1	3.3	5.9	15.2	12.6
		2	2.2	448.5	233.3	3.7
		3	7.6	12.9	5.9	10.5
Transition/transversion rate ratio	Purines	1,2,3	9.6	19.1	18.3	15.6
		1	4.0	5.9	42.1	12.5
		2	9.4	709.1	1000.0	9.6
		3	12.6	26.3	13.5	17.8
	Pyrimidines	1,2,3	13.0	25.5	10.9	22.0
		1	10.8	22.9	0.0	47.3
		2	1.6	1000.0	220.2	6.3
		3	18.0	25.3	10.6	24.5