FIG 4.

Circos plot of heatmaps of SNPs in four lineages and their frequencies. The frequency of each SNP was transformed to the base 2 logarithm, corresponding to color (high frequency, yellow; low frequency, navy), and the changes of SNP frequency during serial passages were seen from inside to outside the Circos plot (red arrow). A heatmap cell of four lineages was arranged clockwise from VP1 to NSP5/6, showing the locations of SNPs on genome segments. Lineages subjected to the stronger bottleneck effect (0.001MOI) increased the number of SNPs at the later stage of virus passage (brightly colored cells [orange or yellow] increased after cycle 3 or 4), and several SNPs randomly appeared and disappeared.