Identification of groups of identical or nearly identical envelope sequences in breast milk of lactating, chronically SIV-infected rhesus monkeys. Trees were inferred by maximum likelihood methods . Cell-associated and cell-free blood virus quasispecies env sequences are indicated with closed and open squares, respectively, and cell-associated and cell-free milk virus quasispecies env sequences are indicated with closed and open circles, respectively. Bayesian posterior probabilities are shown above the branch and bootstrap support values are shown in italics below the branch. Sequences are shown for three chronically infected rhesus macaques: 206 (week 74 after SIV infection), 402 (week 67 after SIV infection), and 403 (week 49 after SIV infection).