frumuskipting

Frumuskipting, literally "cell division" in Icelandic, is the process by which a cell reproduces by forming two or more daughter cells. In multicellular organisms it underpins growth, development, tissue renewal, and asexual reproduction, while in unicellular organisms it is the basis of propagation.

In prokaryotes the process is typically binary fission: the chromosome is replicated, each daughter DNA attaches to the cell membrane, and the cell elongates before a septum splits the cell into two genetically identical offspring. Regulation is simpler and often tied to growth rate.

In eukaryotes, division usually involves mitosis followed by cytokinesis. Before division, cells enter interphase (G1, S, G2), during which DNA is replicated. Mitosis distributes replicated chromosomes into two nuclei, and cytokinesis completes cell separation to form two distinct daughter cells.

Mitosis is subdivided into prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis. A spindle of microtubules and motor proteins assembles, chromosomes condense, align at the metaphase plate, and sister chromatids separate to opposite poles.

Meiosis, by contrast, consists of two sequential divisions (meiosis I and II) with homologous chromosomes pairing and crossing over in prophase I. This yields four genetically diverse haploid gametes, essential for sexual reproduction.

Cell-cycle regulation involves checkpoints and proteins such as cyclins and CDKs, with tumor-suppressors like p53 helping prevent division when DNA is damaged. Abnormal regulation can lead to cancer and aneuploidy. Therapeutics often target mitosis or DNA replication.