Fragmentation of nucleus in a cell is termed as

Fragmentation of nucleus in a cell is termed Karyorrhexis.
Karyorrhexis is the destructive fragmentation of the nucleus of a dying cell whereby its chromatin is distributed irregularly throughout the cytoplasm.
It is usually preceded by pyknosis and can occur as a result of either programmed cell death, cellular senescence, or necrosis. In apoptosis, the cleavage of DNA is done by Ca²⁺ and Mg²⁺ -dependent endonucleases.