The induction and characterization of chromosomal translocations in anopheles Gambiae species A

With the possibility of their eventual use as control agents in mind, attempts were made to isolate and characterize reciprocal chromosomal translocations in species A of the Anopheles gambiae complex. Translocations were induced in males with X-rays and determined by testing for the occurrence of inherited partial sterility. Hatching rate was the principal criterion used for the designation of karyotype. Young males of a Y-autosomal translocation line (TYF-5) were re-irradiated with X-rays at 4000 rads. Several further interchanges were isolated. Among 120 tested F 1 males, four 3-chrornosome double translocation lines were obtained. These lines were found to transmit their characteristic partial sterility (75%) to all their sons when outcrossed to the wild-type, but none of the daughters inherited partial sterility. Comparative studies showed that 3-chromosome doubly translocated males displayed fitness comparable with the wildtype males. Among 92 F1 daughters tested, 8 lines showing regular inheritance of partial sterility were established. In 5 of these lines the presence of translocations was confirmed cytologically. Four were shown to involve autosome-autosome translocations and one involved an X-autosome interchange. The fertilities of these lines were found to be significantly higher than 50%. The merits of using comparatively low radiation dosage are discussed and tested by attempting to induce translocations using only 1,500 rads. From a resulting number of 154 F1 males and females which were outcrossed 7 partially sterile lines were isolated. One of these proved to be a reciprocal interchange between the two autosomes. The remaining 6 lines, when outcrossed to the wild-type, showed a rather low frequency of semisterility. Efforts were made to produce autosomal translocation homozygotes, bllt without success. For all the 5 lines investigated, data obtained from hatching rates of intercrossed heterozygotes suggested that translocation homozygotes would be lethal. In future isolation of autosomal translocation homozygotes it will be essential to employ a team of workers to perform all the requisite tasks of creating, selecting and evaluating strains suitable for genetic control purposes. The probable effectiveness of male-linked translocations is discussed in the light of experimental experiences.