mitosi

Mitosi, known in English as mitosis, is the division of a eukaryotic cell's nucleus that ensures equal distribution of the chromosomes into two genetically identical daughter nuclei, typically followed by cytokinesis which divides the cytoplasm. The process is part of the cell cycle and underlies growth, tissue repair in multicellular organisms, and asexual reproduction in many single-celled eukaryotes. Mitosis is traditionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis.

In prophase, chromatin condenses into visible chromosomes; the nucleolus disappears; the mitotic spindle forms outside the nucleus as microtubules attach to kinetochores. In prometaphase, the nuclear envelope breaks down and microtubules attach to kinetochores. During metaphase, chromosomes align at the metaphase plate with sister chromatids held together by cohesin. In anaphase, sister chromatids separate and are pulled toward opposite poles by shortening microtubules and motor proteins; in telophase, the chromosomes de-condense and a new nuclear envelope forms. Cytokinesis then splits the cytoplasm, producing two daughter cells; in animal cells a contractile actin ring creates a cleavage furrow, whereas plant cells form a cell plate that becomes separating cell walls.

Mitosis is regulated by the cell cycle machinery, including cyclin-dependent kinases and various checkpoints such as the spindle assembly checkpoint that monitors chromosome attachment to the spindle. Errors in mitosis can cause aneuploidy and have been linked to diseases including cancer. The process is distinct from meiosis, which reduces chromosome number and increases genetic variation.