Fluorescent light micrograph of a cell during the metaphase stage of mitosis (nuclear division). Mitosis is the formation of two daughter nuclei from one parent nucleus. Fluorescent markers have been used to highlight alpha tubulin (blue), a component of microtubules, cohesin (red), which holds sister chromatids together, and topoisomerase II (green), an enzyme that plays a role in the condensation of chromosomes prior to mitosis. During metaphase the chromosomes align along the centre of the cell. In the next stage the sister chromatids of each chromosome are pulled to opposite poles by the mitotic spindle, the main component of which are microtubules.