Genetic distance and probable ancestral relationships among Tlr4 genes of 35 Mus musculus strains. Numbers within circles denote strains, in accordance with the legend to Table 1. Numbers adjacent to arrows indicate the mutational distance (number of mutations separating each strain from its presumed ancestor), with reference to both coding and noncoding substitutions listed in Table 1. Arrows point in the direction of descent, and their lengths are proportional to distance. Dotted lines suggest introgression, given the similarity of the haplotypes observed. The symbol → denotes the likelihood of an intermediate form before interbreeding of strains.