Changes in NOR activity pattern in the presence of supernumerary heterochromatin in the grasshopper Eyprepocnemis plorans.

Nucleolus organizer region (NOR) activity was analysed in four types of males of the grasshopper Eyprepocnemis plorans, possessing two kinds of supernumerary heterochromatin: a B chromosome and a supernumerary chromosome segment proximally located on the smallest autosome (S11). In males lacking extra heterochromatin, the four active NORs located on the S9, S10, S11, and X chromosomes showed independent activity patterns, but several kinds of dependence appeared in the presence of supernumerary heterochromatin. Furthermore, temporal changes in NOR activity were observed during the first 2 weeks of adult life in standard males but not in males carrying supernumerary heterochromatin. It is suggested that all these effects are related to the DNA content of both types of extra heterochromatin.