SYNTHETIC LETHALITY AND SEMI-LETHALITY AMONG FUNCTIONALLY RELATED MUTANTS OF DROSOPHILA MELANOGASTER

sex-linked mutant deep orange (dor) of Drosophila melanogaster is Tzonsible for a peculiar type of female sterility: mutant females produce no progeny when crossed to mutant males but yield some offspring (heterozygous daughters) when mated to wild-type males (MERRELL 1947). The effects of this mutant on embryonic development have been extensively studied by COUNCE (1956a) and more recently by HILDRETH and LUCCHESI (1967). In addition to the sterility phene, dor alters the pigmentation of the eyes (which are orange in color) and confers an abnormal spectrum of relative pteridine concentrations. An unusual characteristic of dor is that isoxanthopterin appears to be accumulated by mutant females (COUNCE 1957). During the course of preliminary investigations into the biochemical basis of dor female-sterility, art attempt was made to prevent the accumulation of isoxanthopterin in mutant females by genetic means. This resulted in the discovery of a highly specific synthetic lethal system involving dor and a non-allelic third chromosome mutant, rosy (ry) . The dor-ry system is similar to three other synthetic lethal systems, previously described in D. melanogaster: purpleoid (pd) and Purpleoider (Pdr) (BRIDGES 1922; as cited in BRIDGES and BREHME 1944) ; prune (pn) and Prune-killer (K-pn) ( STURTEVANT 1956) ; and Henna-recessiue-3 (Hnr3) and rosy (ry6) (TAIRA 1960; GOLDBERG, SCHALET and CHOVNICK 1962). A search was undertaken for the purpose of uncovering additional interactions among some of the mutants mentioned above. Since six of the latter affect eye color and/or pteridine levels, a number of other eye color mutants were tested. In addition, the female sterile mutant fused (fu) , similar in many respects to dor (although allowing lethal embryos to develop further than dor embryos (COUNCE 195613) ). was used in