Abstract Despite vast differences between organisms, some characteristics of their genomes are conserved, such as the nucleolus organizing region (NOR). The NOR is constituted multiple, highly repetitive rDNA genes, encoding catalytic ribosomal core RNAs which transcribed from 45S units. Their precise sequence information and organization remain uncharacterized. Here, using a combination long- ...

Plants combining the cytoplasm of Nicotiana debneyi and the 48 chromosomes from N. tabacum are male sterile. Early backcross generations of the amphidiploid hybrid to male N. tabacum produced a great variety of plants from which a series of phenotypes with characteristic flower forms and transmission rates have been isolated. Type 1A possesses completely feminized stamens and deeply split corol...

Mitosis in the amebo-flagellate Naegleria pringsheimi is acentrosomal and closed (the nuclear membrane does not break down). The large central nucleolus, which occupies about 20% of the nuclear volume, persists throughout the cell cycle. At mitosis, the nucleolus divides and moves to the poles in association with the chromosomes. The structure of the mitotic spindle and its relationship to the ...

In Allium ursinum meiotic pairing of homologues is always incomplete; a proximal region on each bivalent remains regularly unsynapsed even in late pachytene. The spatial correlation of the unsynapsed region with the kinetochore suggests that the kinetochore itself exerts an inhibitory effect on synapsis in its vicinity. This can be interpreted as the cytological basis of the 'centromere effect'...

The structure of nuclei of Astasia longa in synchronized cultures was examined at the light- and electron-microscope levels. Three types of nuclei, differing mainly in chromatin conformation, were observed during interphase and were tentatively classed in the G1, S and G2-periods. The fibrillar nucleolar regions exhibited a most complex organization and appeared to consist of convoluted, coarse...