VIRAL QUASI-SPECIES AND RECOMBINATION

Virus populations are complex ensembles of distinct but related genome s (so called quasi-species). Mathematical descriptions of viral quasi- species focus on point mutations as the principal source of variation. However, retroviruses (and many other viruses) are able to recombine their genomes. We study a mathematical model of viral quasi-species dy namics which incorporates both point mutation and recombination. We sh ow that for low mutation rates recombination can reduce the diversity of the quasispecies and enhance overall fitness. For high mutation rat es, however, recombination can push the quasi-species over the error t hreshold, and thereby cause a loss of all genetic information. Finally , recombination introduces bistability to the quasi-species; if the fr equency of an advantageous mutant is below a certain threshold, it wil l not be selected.