Towards a population genetics of microorganisms: The clonal theory of parasitic protozoa.

Over the past 15 years, molecular investigations, including the study of isozymes and DNA markers, have provided much information on the genetic variation, population structure, breeding system and other population characteristics of parasitic protozoa. For some parasitic protozoa, but not for others, the evidence indicates that their reproduction is prevailingly clonal. In this article, Michel Tibayrenc and Francisco Ayala propose that the issue of whether the predominant mode of reproduction of a given micro-organism is clonal or sexual can only be settled by population genetics information, and they summarize evidence favoring a clonal population structure for a number of parasitic protozoa.