A SUCCESSFUL BACKCROSS IN TRYPANOSOMA-BRUCEI

Genetic exchange can take place between different strains of Trypanosoma brucei ssp. when they are cotransmitted via the tsetse fly vector, but the mechanism and limits of compatibility between strains are ill-defined as yet. Following the recovery of several hybrid genotypes with single drug resistance from a cross of drug resistant parental strains, we attempted a series of backcrosses and F1 crosses, selecting hybrids by double drug resistance. Of 4 backcrosses, one produced hybrid progeny, the analysis of which is presented here, but none of the 4 F1 crosses produced hybrid progeny. However, among experimental flies from the 8 crosses, although there were large numbers of salivary gland infections, very few consisted of a mixture of parental clones, a prerequisite for mating. In the successful backcross both parents were diploid, but none of the crosses involving triploid clones produced hybrid progeny. The hybrid-secreting fly from the backcross contained a mixture of hybrid and parental clones. The hybrid clones had approximately 3n DNA contents relative to the 2n parental clones and fell into 2 groups with respect to restriction site polymorphisms in kinetoplast DNA maxi-circles. Fingerprinting by random PCR amplification using 8 different arbitrary primers showed minor variation between the hybrid clones.