Figure 1.

Midpoint-rooted phylogenetic tree of env sequences for the viral populations collected from both twins. Numbers above and below branches indicate Maximum Likelihood (ML) bootstrap proportions and Bayesian posterior probabilities (as percentages), respectively. Reference sequences (see main text for details) from the US are indicated by a star. Tree branch colors represent three sampled time points in the env sequences for twin A and twin B (green: 09/15/1998, blue: 10/13/1998 and purple: 11/10/1998).