Maximum likelihood tree of South American F1 and BF1 recombinant strains (Black squares) and reference strains (location is shown in each sequence name) inferred from C2-C3 env region. Gray circles show the newly sampled strains from Brazil. Trees were rooted using HIV-1 HXB2 isolate. The approximate likelihood-ratio test (aLRT) values of ≥ 70% are indicated at nodes. The scale bar represents 0.01 nucleotide substitution per site.