ANALYSIS OF A NEW GENETIC CROSS BETWEEN 2 EAST-AFRICAN TRYPANOSOMA-BRUCEI CLONES

Two clones of East African Trypanosoma brucei, with distinct homozygou s isoenzyme patterns for one of three enzymes examined, were cotransmi tted through the tsetse fly vector Glossina morsitans centralis. Flies with mature infections were individually fed on mice and the subseque nt bloodstream form populations analysed for the presence of hybrid tr ypanosomes by isoenzyme analysis. Several combinations have previously been detected using this approach (Schweizer, Tait & Jenni, 1988; Ste rnberg et al. 1989). Four clones were isolated from one of the hybrid- containing populations. They showed a hybrid phenotype, as would be ex pected for the F1 progeny in a diploid Mendelian system. The analysis of the progeny clones, using two gene probes which detect restriction fragment length polymorphisms between the two parental stocks, showed that alleles had segregated at each locus and given rise to three diff erent non-parental combinations of alleles in the hybrid progeny. Char acterization of the hybrid progeny clones by PFGE (pulsed field gradie nt gel electrophoresis) revealed that all progeny clones were recombin ant for the intermediate size chromosomes. From the analysis of the se gregation of the larger chromosomes, marked by PGK (phosphoglycerate k inase) and CP (cysteine protease) gene probes, it was inferred that th e progeny clones did not result from a direct fusion of diploid cells. Results with the PGK probe fit into a classical system with meiosis a nd subsequent fusion of the nuclei to form diploid progeny. On the oth er hand, blots with the CP probe as well as some of the ethidium bromi de stained PFGE gels revealed the existence of non-parental size chrom osomes in some of the hybrid progeny. This phenomenon was observed pre viously (Gibson, 1989) and further investigation is required to elucid ate the mechanism.