On the cell lethality of Notch and Abruptex mutations of Drosophila melanogaster

Abstract

Cell lethality of N55e11, N8, Ax59b8.1, and Ax59d5 mutations of the Notch complex locus of Drosophila melanogaster was tested by inducing homozygous mutant clones in heterozygous flies with X-ray irradiation of first instar larvae aged 24–48 hours. The X chromosome carrying the lethal mutant was marked with yellow (y) and white (w), and the homologue was marked with singed-3 (sn3) and white. In flies heterozygous for Notch mutations no twin-spots and only a few yellow spots were observed, and the frequency of singed spots was higher than in the controls. This indicates that the Notch mutations are primary cell lethals. In flies heterozygous for Abruptex mutations yellow spots and twin-spots were abundant, although not as frequent as in the control flies. The frequency of singed spots was above the level of the controls. This indicates that Abruptex mutations are not primary cell lethals, but that their lethal action is probably restricted to some particular tissue, i.e. they may be focus lethal mutations. The wild allele carried by the duplication Dp(1;2)51b7, N+ probably fully restores the viability of homozygous Notch cells, but does not fully restore the viability of homozygous Abruptex cells. This reflects the fact that Notch mutations are amorphic while Abruptex mutations are antimorphic.