Karyokinesis

Karyokinesis is the process by which a eukaryotic cell's nucleus divides, distributing the cell's genetic material into two separate nuclei. It is distinct from cytokinesis, the division of the cytoplasm, and occurs during cell division in both mitosis and meiosis.

In mitosis, karyokinesis is accompanied by chromosomal condensation and the formation of the spindle apparatus. The chromosomes align at the metaphase plate, sister chromatids separate in anaphase, and daughter chromosomes are pulled toward opposite poles. The nuclear envelope disassembles in prophase and re-forms around the daughter nuclei in telophase.

In meiosis, there are two successive nuclear divisions. Meiosis I separates homologous chromosomes, reducing the chromosome number, and meiosis II resembles mitosis, separating sister chromatids. This sequence produces four haploid gametes and, through recombination, increases genetic diversity.

Spindle microtubules, kinetochores, and centrosomes coordinate chromosomal movements. Errors in karyokinesis can cause aneuploidy or polyploidy, with potential developmental consequences. While cytokinesis partitions cytoplasm, karyokinesis ensures the correct distribution of nuclear material. The term contrasts with the historical concept of cytoplasmic division and has roots in 19th-century descriptions of mitosis.