Karyokinese

Karyokinesis is the process by which a eukaryotic cell's nucleus divides, distributing the chromosomes into daughter nuclei. It encompasses mitosis and meiosis and is distinct from cytokinesis, the division of the cytoplasm that typically accompanies or follows nuclear division.

During karyokinesis, chromosomal DNA condenses into visible chromosomes, the spindle apparatus forms, and chromosomes are aligned at the metaphase plate before being separated to opposite poles. In mitosis the result is two genetically identical diploid nuclei; in meiosis, two successive divisions generate four haploid nuclei with shuffled genetic content. In many organisms, the nuclear envelope breaks down during prophase (open mitosis) to permit spindle access, whereas some fungi and algae perform closed mitosis with an intact envelope.

Following chromosome separation, the nuclei are reorganized around the separated chromosome sets, and cytokinesis partitions the cytoplasm to form separate daughter cells. Karyokinesis can occur without cytokinesis in certain conditions, producing multinucleate or polyploid cells through endomitosis or related cell-cycle variations.

Karyokinesis occurs in eukaryotes; prokaryotes do not undergo true nuclear division, as they lack a defined nucleus. The process is tightly regulated by the cell cycle, including cyclin-dependent kinases and checkpoints that ensure genome integrity before division.

Historically, the term karyokinesis was introduced to distinguish nuclear division from cytoplasmic division. The concept and its stages were described in the late 19th century by Walther Flemming, whose work on mitosis established foundational terminology for cell reproduction.