Nucleolus organizer chromosomes in a teleostean species of tetraploid origin,iCyprinus carpi/iio/i

摘要

The presence of nucleolus organizer regions (NORs) was investigated in a teleostean species of tetraploid origin, Cyprinus carpio, by means of Ag-staining. Even if four NOR-bearing chromosomes exist, only two of them are normally active. This evidence supports the hypothesis that, in this species, diploidization of gene expression may be due to a reduction in the rate of rRNA transcription.