mitosis The normal process of nuclear division by which two daughter nuclei are produced, each identical to the parent nucleus. Before mitosis begins each chromosome replicates; these daughter chromosomes then separate during mitosis so that one duplicate goes into each daughter nucleus. The result is two daughter nuclei, each with an identical complement of chromosomes and hence of genes. Mitosis is generally divided into four phases: prophase, metaphase, anaphase, and telophase. During prophase, chromosomes become visible within the nucleus because they shorten, thicken, and coil up as a spiral. Each chromosome is longitudinally double except in the region of the centromere, and each single strand of the chromosome is called a chromatid. The nucleolus and nuclear envelope disappear. In metaphase the chromosomes move within the spindle connecting the two centrosomes (formed by division of the centriole into two at the start of prophase, and the subsequent moving apart of these two daughter centrioles). The chromosomes finally arrange themselves along the equator of the spindle. During anaphase, the two chromatids making up each chromosome separate as the centromere becomes functionally double, and are thus converted to independent chromosomes moving to opposite poles. During telophase, the spindle disappears, a nuclear envelope reappears around each of the two groups of daughter chromosomes, the chromosomes return to their extended state, and the nucleoli reappear. This is usually followed by cytoplasmic division (cytokinesis) into two parts by a cleavage furrow. The final result is two daughter cells with identical nuclear contents. Compare MEIOSIS.