Mitosis

Once the cell has copied its DNA, just before it divides, the 46 chromosomes - usually long strings in the nucleus - coil up into compact bundles. The edge of the nucleus then dissolves, and temporary protein scaffolding appears in the cell: the spindle apparatus. The chromosomes use this to line up in the centre of the cell. The chromosomes then split and one of each duplicate chromosome moves to the opposite end of the cell. Finally, the cell narrows in the middle and divides.