Production of X0 clones in XX females ofDrosophila

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Abstract
Summary: The experiments reported here are aimed at determining whether mutations deleting the function of theSex-lethal(Sxl) gene are able to suppress the lethality of X0 clones, induced in females after the time when the state of activity ofSxlis irreversibly fixed by the ratio of the number of X chromosomes to sets of autosomes (X: A). This analysis was carried out by comparing the frequency of induced male clones (X0 constitution) inSxlfLS/ + andSxl+/Sxl+females, following irradiation at blastoderm and larval stages. The genotype used in these experiments, however, could also give rise to 2X; 2A cells homozygous forSxlfLS, and such cells would also differentiate male structures. To minimize this possibility, we have constructed a genotype made up of a ring and a rod X chromosome. In such ring-rod females the production of 2X; 2A clones homozygous forSxlfLSis a rather rare event, if possible at all. X0 male clones were produced in both types of females following irradiation at blastoderm stage, while X0 male clones were only observed inSxlfLS/ + females when irradiation took place at larval stage. In this latter case, the only X0 male clones were those that contained theSxlfLSmutation. These results support the idea of Sánchez & Nöthiger (1983) that the X: A signal irreversibly sets the state of activity ofSxlat blastoderm stage, and in addition show that X0 clones generated after that time are viable if they contain aSxl−mutation. These results are compatible with the idea ofSxlbeing the only gene that responds to the X:A signal.