A SUCCESSFUL BACKCROSS IN TRYPANOSOMA-BRUCEI

Genetic exchange can take place between different strains of Trypanoso ma 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 wit h single drug resistance from a cross of drug resistant parental strai ns, we attempted a series of backcrosses and F1 crosses, selecting hyb rids 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 fr om the 8 crosses, although there were large numbers of salivary gland infections, very few consisted of a mixture of parental clones, a prer equisite for mating. In the successful backcross both parents were dip loid, but none of the crosses involving triploid clones produced hybri d progeny. The hybrid-secreting fly from the backcross contained a mix ture of hybrid and parental clones. The hybrid clones had approximatel y 3n DNA contents relative to the 2n parental clones and fell into 2 g roups with respect to restriction site polymorphisms in kinetoplast DN A maxi-circles. Fingerprinting by random PCR amplification using 8 dif ferent arbitrary primers showed minor variation between the hybrid clo nes.