The grasshopper X chromosome. II. Negative heteropycnosis, transcription activities and compartmentation during...

The X chromosome can be identified with the light microscope throughout all stages of the gonial cell cycle (including interphase) in the grasshopper Brachystola magna. At gonial mitotic stages the X chromosome gives the appearance of being undercondensed or negatively heteropycnotic. At interphase the X projects out from the body of the nucleus.--Examination with the electron microscope reveals that the X is compartmentalized at least two gonial cell cycles prior to the entry of the cells into meiotic prophase. The membrane layers that envelope the X chromatin at interphase remain associated with the X chromosome throughout gonial mitotic stages providing the ultrastructural basis for the apparent negative heteropycnosis observed with the light microscope.--The X chromosome is inactive in RNA synthesis during gonial mitotic stages but is hyperactive in RNA synthesis when compared to autosomes at gonial interphase.--X-chromosome condensation which reaches its maximum at premieotic interphase is initiated at or prior to the pre-pentultimate gonial division.