Clonal variation of gene expression as a source of phenotypic diversity inparasitic protozoa

Within a cellular clone, individual cells can express different members of a gene family. If the difference in expression is transmitted to daughter c ells, 'phenotypic clones' are formed. Such clonal phenotypic variation has evolved independently in phylogenetically distant parasitic protozoa under similar selective pressure: the need for phenotypic diversity at several st eps of their life cycle. Here, I review clonal phenotypic variation process es, outline their role in parasite biology and argue that clonal phenotypic variation is complementary to sexual reproduction as a source of phenotypi c diversity.