Mitosis Created 2026-10-14 Updated 2026-10-14
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Mitosis allocates copied chromosomes to daughter cell nuclei. The spindle apparatus aligns sister chromatids before separation in anaphase.
The copying has already occurred during S phase, before mitosis. Nuclear chromosome segregation and cytokinesis, the partition of the cytoplasm, are distinct processes: two daughter cell nuclei can form inside one undivided biological cell.[ref]
The original cartoon follows a hypothetical diploid animal biological cell with . Its two homologous chromosome pairs are and ; upper- and lower-case letters identify homologues, not dominant and recessive alleles. In prophase and metaphase, each replicated chromosome contains two sister chromatids: four replicated chromosomes contain eight chromatids, rather than eight replicated chromosomes. The X shape depicts two associated copies, not the shape of every chromosome throughout the cell cycle.
Figure 1.
Mitosis partitions replicated chromosomes; cytokinesis separates the daughters
. Original schematic of a hypothetical animal biological cell, drawn with open mitosis. Colors and letters follow the four original chromosomes; paired strokes represent sister chromatids. Every anaphase pole and each completed daughter receives . Green lines represent selected spindle apparatus microtubules; dark dots mark centromere regions. The intermediate prometaphase is described below. Geometry and arrow spacing are illustrative, not recorded images or elapsed times. Details.
This open mitosis cartoon shows nuclear envelope breakdown and reassembly. Closed mitosis in some yeasts retains the nuclear envelope while daughter chromosomes separate inside it; the cartoon is therefore not a universal cellular architecture.[ref]
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