Confocal light micrograph of a human breast cell undergoing mitosis (nuclear division, centre). 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 (green), a component of microtubules. The cell is 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.