Pyknosis, or karyopyknosis, is the irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis or apoptosis. It is followed by karyorrhexis, or fragmentation of the nucleus. Pyknosis (from Greek pyknono meaning "to thicken up, to close or to condense") is also observed in the maturation of erythrocytes (a red blood cell) and the neutrophil (a type of white blood cell). The maturing metarubricyte (a stage in RBC maturation) will condense its nucleus before expelling it to become a reticulocyte. The maturing neutrophil will condense its nucleus into several connected lobes that stay in the cell until the end of its cell life.
^Kumar V, Abbas A, Nelson F, Mitchell R. (2007). "Robbins Basic Pathology". Robbins Basic Pathology (8th ed.): 6, 9–10.Unknown parameter |table= ignored (help)
^Kroemer G, Galluzzi L, Vandenabeele P, et al. (January 2009). "Classification of cell death: recommendations of the Nomenclature Committee on Cell Death 2009". Cell Death Differ.16 (1): 3–11. doi:10.1038/cdd.2008.150. PMC2744427. PMID18846107.