Generally there is a single nucleus per cell (mononucleate conditions), but more than one nucleus (polynucleate condition) may be found in certain special cases. There may be many nuclei in a syncytium, which is formed due to fusion of cells. A similar multinucleate situation is found in coenocytes commonly found in plants. A coenocyte results by repeated nuclear divisions without cytokinesis.

There are variations with respect to shape of nucleus also. It may be spherical, oval to flattened lobe or irregular in shape. In most cases it has a regular outline, but may also have irregular outline. Shape of nucleus also depends on the cell. In spheroid, cuboid or polyhedral cells, nucleus is usually spheroid. In cylindrical, prismatic or fusiform cells, nucleus is ellipsoid. Irregular nuclei are sometimes found in some neutrophylls or leukocytes and branched nuclei are sometimes found in glandular cells. In still other cases like spermatozoa, pyriform or lanceolate nuclei may be found.