Experimental Parasitology

Genetic exchange between cells of Trypanosoma brucei that occurs in the tsetse fly vector (Jenni et al. 1986) is an important part of the life cycle that contributes significantly to genetic diversity of these human pathogens (Gibson and Stevens 1999). Indirect observations have also indicated the presence of sexuality during the development of Trypanosoma cruzi (Bogliolo et al. 1996; Stothard et al. 1999) and Trypanosoma carassii (Zajı́c̆ek 1991). However, a thorough search for this process in related Leishmania failed to detect the recombination process in its vector (Panton et al. 1991), although rare natural hybrids have been reported (Belli et al. 1994; Banuls et al. 1997). A better understanding of genetic exchange that apparently has important implications for pathogenicity and epidemiology of sleeping sickness and Chagas disease would also provide us with a novel way of combining the limited number of markers (Clayton 1999) currently available for genetic manipulations of Kinetoplastida. Crithidia fasciculata is a monoxenic model trypanosomatid, the Steinert and UC strains of which have existed in culture for decades. For C. fasciculata, a relatively high frequency of appearance of mutants with multiple resistance has