We next investigated the fate of these recombinants with respect to their establishment in the natural HIV-1 population. The fixation of a recombinant gene within a population is dependent on the interplay of multiple factors. Nevertheless, an obligatory component of evolution is undoubtedly the elimination by purifying selection of viruses that express dysfunctional proteins. To evaluate how profoundly this aspect of natural selection might influence the pattern of breakpoints generated by the mechanism of recombination, we determined the relative functionality of a subset of recombinant env genes.