Abstract
From the fact that the number of NORs shows an extreme variation between the individuals of one species, it is concluded that a mechanism should exist which ensures the supply with ribonucleoproteins in the cell. Reports are reviewed dealing with this subject and two original studies are presented.—The number of satellite associations, and NOR-silver staining, were studied in a human female with 13/13 Robertsonian translocation and her relatives. The proband showed a higher association frequency and a more intensive silver staining of chromosome no. 22 when compared to her parents and her sister. It seems likely that this difference was caused by the loss of two NORs after the fusion of both chromosomes no. 13.—In a second study, 22monosomic mitoses of a human meningioma were compared with chromosomal normal fibroblasts of the same patient. The meningioma cells showed an increased association frequency and a higher silver content of chromosome no. 14. These results also indicate that the loss of one or even more NORs can be compensated by a higher activity of the remaining NORs.
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