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. 2011 Sep;1(1):a006841. doi: 10.1101/cshperspect.a006841

Figure 4.

Figure 4.

HIV-1 origins. The phylogenetic relationships of representative SIVcpz, HIV-1, and SIVgor strains are shown for a region of the viral pol gene (HIV-1/HXB2 coordinates 3887–4778). SIVcpz and SIVgor sequences are shown in black and green, respectively. The four groups of HIV-1, each of which represents an independent cross-species transmission, are shown in different colors. Black circles indicate the four branches where cross-species transmission-to-humans has occurred. White circles indicate two possible alternative branches on which chimpanzee-to-gorilla transmission occurred. Brackets at the right denote SIVcpz from P. t. troglodytes (SIVcpzPtt) and P. t. schweinfurthii (SIVcpzPts), respectively. The phylogenetic tree was estimated using maximum likelihood methods (Guindon and Gascuel 2003). The scale bar represents 0.05 nucleotide substitutions per site.