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Notes: Summary Diplo-X flies homozygous for the transform-er-2 ts (tra-2 ts) mutation develop into females at 16° C, while they develop into males at 29° C (Belote and Baker 1982). By means of this conditional mutation, we have carried out a detailed analysis of the development of the genital disc. Temperature shifts between 16 and 29° C, in both directions, and temperature pulses at 29° C, have been applied during the larval growth of tra-2 ts homozygous diplo-X flies, and the external derivatives of the genital disc have been analysed. Genital discs shifted from 16 to 29° C rapidly lose their capacity to differentiate female genital structures, while they become able to differentiate male genital structures whose inventory is more complete the earlier in larval development the temperature shift is carried out; moreover, duplicated male genital structures were observed. In the shift from 29 to 16° C, the genital disc loses its capacity to differentiate male genital structures, while it becomes able to differentiate female genital structures. The inventory of male structures is smaller, and the inventory of the female structures is more complete, the earlier in larval development the temperature is shifted. No duplicated female or male genital structures were observed in the downshift experiment. With respect to the analia, the shift from 16 to 29° C resulted in the quick formation of pure male anal plates, while in the opposite shift the formation of pure female anal plates occurred gradually. Moreover, the time course for the dorsal and ventral anal plates to show normal female phenotype was different: when the dorsal anal plates were completely normal, it was still possible to find incomplete ventral anal plates. In the pulse experiment at 29° C, the genital disc is able to differentiate both female and male genital structures, although the inventory of the latter ones was not complete. In addition, the capacity of the genital disc to differentiate male genital structures depended on the duration of the temperature pulse. The anal plates were always female, although they showed a reduction in their size, the ventral female anal plate being more affected than the dorsal one. No male anal plates were observed. The results have revealed that the genital disc follows a sequence in its capacity to differentiate female or male adult structures. We suggest that this sequence reflects the sequence of determination events occurring in the genital disc during its larval growth. In addition, results shown here provide evidence for the existence in the female genital primordium of a set of cells capable of giving rise either to female genital structures (ventral vaginal plates) or to male genital structures (hypandrium and penis apparatus). We also present evidence supporting the previous idea of two primordia for the anal plates.

Notes: Abstract  Crosses between Drosophila melanogaster females and D. simulans males produce viable hybrid females, while males are lethal. These males are rescued if they carry the D. simulans Lhr gene. This paper reports that females of the wild-type D. melanogaster population Staket do not produce viable hybrid males when crossed with D. simulans Lhr males, a phenomenon which we designate as the Staket phenotype. The agent responsible for this phenomenon was found to be the Staket X chromosome (X mel , Stk). Analysis of the Staket phenotype showed that it is suppressed by extra copies of D. melanogaster rDNA genes and that the X mel , Stk chromosome manifests a weak bobbed phenotype in D. melanogaster X mel , Stk/0 males. The numbers of functional rDNA genes in X mel , Stk and X mel , y w (control) chromosomes were found not to differ significantly. Thus a reduction in rDNA gene number cannot account for the weak bobbed X mel , Stk phenotype let alone the Staket phenotype. The rRNA precursor molecules transcribed from the X mel , Stk rDNA genes seem to be correctly processed in both intraspecific (melanogaster) and interspecific (melanogaster-simulans) conditions. It is therefore suggested that the X mel , Stk rDNA genes are inefficiently transcribed in the melanogaster-simulans hybrids.