Entwicklungsgenetische Untersuchungen an Gynandern vonDrosophila melanogaster

Summary

In ring/rod-X-chromosome heterozygotes the ring-X-chromosome is frequently lost in the early cleavage mitoses. The resulting gynandromorphs are mosaics with female XX- and male XO-areas. The phenotypes of the recessive alleles on the rod-X-chromosome are expressed in the XO-areas.

The genemaroonlike (mal) on the X-chromosome influences the activity of the enzyme aldehyde oxidase. This fact was used to test the cell autonomy of aldehyde oxidase activity by histochemical methods in gynandromorphs of the genotypesR(1)2,In(1)w ^vC/y w mal andR(1)2,In(1)w ^vC/y w sn ³ lz ^50e mal. The results show that in the cells of the imaginal Malpighian tubules the phenotypes ofwhite (w) andmaroonlike (mal) always occur together; XX-cells are pigmented and show aldehyde oxidase activity, whereas colorless XO-cells have no such enzyme activity (Figs. 1 and 2). This cell autonomy of aldehyde oxidase activity most likely applies also to the imaginal gut and the inner genitalia.

The distribution of XX- and XO-areas in the Malpighian tubules, the gut and the inner genitalia was examined in 355 gynandromorphs. Approximately half of the gynanders have Malpighian tubules with an XX/XO-mosaic (Table 1, 2 and 3). A large fraction of the mosaic tubules (62%; Table 4) shows a pattern of alternating small cell clusters of different genotypes. It is supposed that this pattern develops during the formation of the tubes, especially during their elongation. The number of primitive Malpighian cells is estimated to be about 140.

72% of the gynanders have mosaic guts (Table 1 and 5). The border between tissues of different genotypes is found very frequently in the posterior third of the anterior midgut (Fig. 3) and may correspond to the border between the tissues which develop from the anterior and posterior midgut rudiments. The estimates of the numbers of primitive cells for the gut structures are 2–3, as far as the crop, the cardia and the rectal valve are concerned, whereas a number of several hundred is estimated for the anterior as well as for the posterior midgut.

Mosaics were also found in the inner genitalia consisting of combinations of male and female structures. In 16 gynandromorphs the paragonia or the ductus ejaculatorius were mosaic (Fig. 4); i.e. in male structures with XO-genotype areas with aldehyde oxidase activity were found. Nothing is known about the origin of these XX-cells, but the possibility must be considered that in gynandromorphs cells of female genotype can participate in the development of male genital structures.