A NUCLEOLUS ORGANIZER REGION IN A B-CHROMOSOME INACTIVATED BY DNA METHYLATION

Chromosomal DNA methylation patterns were determined in the grasshopper Eyprepocnemis plorans by in situ digestion with Mspl and HpaII. While no methylated regions were observed in standard chromosomes, the B chromosome was methylated in the distal third of its long arm. In this zone the B chromosome had an active nucleous organizer region (NOR) in a male carrying a centric fusion between the B and the longest autosome, and it was not methylated. This NOR, however, was never observed in the active form in nonfused B chromosome, possibly because of methylation of this B chromosome region.