 Some eukaryotic protozoa such as Leishmania major and Trypanosoma cruzi lack the RNAi pathway entirely . Most or all of the components are also missing in some fungi , most notably the model organism Saccharomyces cerevisiae . The presence of RNAi in other budding yeast species such as Saccharomyces <unk> and Candida albicans , further demonstrates that inducing two RNAi @-@ related proteins from S. <unk> facilitates RNAi in S. cerevisiae . That certain ascomycetes and basidiomycetes are missing RNA interference pathways indicates that proteins required for RNA silencing have been lost independently from many fungal lineages , possibly due to the evolution of a novel pathway with similar function , or to the lack of selective advantage in certain niches . 
