Confocal light micrograph of cultured cells from mouse breast cancer tumour tissue. Several cells are undergoing mitosis (nuclear division). Mitosis is the formation of two daughter nuclei from one parent nucleus. Fluorescent markers have been used to highlight DNA (deoxyribonucleic acid, blue) and alpha tubulin (red), a component of microtubules. A cell at lower centre right is in metaphase, with the chromosomes (blue) lined up along the centre of the cell. Two cells, one at upper centre right and one at centre left are in anaphase. The two identical chromatids that make up each chromosome have been separated to opposite ends of the cell. The chromatids are pulled apart by the mitotic spindle, the main component of which are microtubules.