K_a/K_s ratio of different group-specific genes. Data are measured using the genes present in the Bc group (Ba₁, Bt, and Bc₁). (A) Genes present in the Bc group; (B) Genes present in Bc, Gk, Bl, and Bs; (C) genes present in Bc, Gk, Bl, Bs, Bk, and Bh; (D) genes present in all 13 strains.