Fig. 3: Genetic diversity of the predominant Y. pestis group 2.MED3 in Inner Mongolia.

a A maximum likelihood phylogenetic tree, derived from 536 SNPs within the core genome of 775 Y. pestis strains (436 from Inner Mongolia and 339 from adjacent regions), uses the CO92 chromosome as a reference and outgroup. The tree, visualized through GrapeTree, features circles whose sizes correspond to strain counts and color intensities that reflect isolation date—darker shades denote more recent isolations. b A ridge plot illustrates the pairwise SNP genetic distances among strains within the 2.MED3 subgroups. Median distances are highlighted by white vertical lines.