Figure 6. Phylogenetic analysis of MMTV env-like amplicons. ENV1-C, ENV1-T, and ENV2 amplicons (filled triangles) were analyzed to infer their phylogeny with respect to the other exogenous and endogenous betaretrovirus nucleotide sequences (see Materials and Methods for further details). The close relationship between the tree MMTVels amplicons and both MMTV and HMTV was confirmed at the phylogenetic level, given that all the sequences grouped together in the same clade that was statistically supported by the maximum bootstrap value. The amplicons were instead not related to any of the HERV-K HML groups’ sequences, which were clearly clustered in a different phylogenetic clade. Evolutionary relationships were inferred by using the maximum likelihood method and the Kimura-2-parameter model, and the resulting phylogeny was tested using the Bootstrap method with 100 replicates. The length of branches indicates the number of substitutions per site.