Phylogenetic analysis of HIV-1 RT of 132 RT sequences from five mother-infant pairs, including B, C, D, F and H. The neighbor-joining tree is based on the distance calculated between the nucleotide sequences from the five mother-infant pairs. Each terminal node represents one RT gene sequence. The numbers on the branch points indicate the percent occurrence of branches over 1,000 bootstrap resamplings of the data set. The sequences from each mother formed distinct clusters and are well discriminated and in confined subtrees, indicating that the variants from the same mother-infant pair are closer to each other than to other sequences and that there was no PCR cross-contamination. These data were strongly supported by the high bootstrap values indicated on the branch points.