Studying the genetic relatedness of multiple single-virion amplicons by using a limiting-dilution RT-PCR technique provides useful insight into the evolution of genetic diversity of HIV-1 populations.  The figure illustrates that chronically infected patients initiating treatment have highly diverse populations prior to therapy.  Even though rapid viral load declines occur after initiation of treatment (shown by the arrow), phylogenetic analysis has revealed that HIV-1 population structure post-treatment is indistinguishable from pretherapy samples, even following greater than 100-fold decreases in plasma HIV-1 RNA levels.  These results suggest a large replicating HIV-1 population in infected persons.