Chromosomal basis of dosage compensation in Drosophila. 4. Hyperactivity of the polytene X-chromosome in male Drosophila kikkawai and Drosophila bipectinata

Abstract

The functional morphology and the transcriptive activity of the male X-chromosome in Drosophila kikkawai and D. bipectinatahave been exarnined. In both these species of the melanogaster species-group, the X-chromosome in the salivary glands of the male Iarvae is enlarged and pale stained as in Drosophila melanogaster, ³H-uridine autoradiography shows that in both the species, the relative rate of RNA synthesis by the single X of the male is similar to that by the two X's of female. The results indicate that: (a) the enlargement and pale staining of the single X in the larval salivary glands of [he male is of general occurrence in the genus Drosophila, and (b) despite the changes in the configuration and organization of the X-chromosome in these species (that have taken place during their evolution), the hyperactivity of the male X and therefore, dosage compensation for X-linked genes, has remained unchanged.