Fluorescent light micrograph of a cell in metaphase 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 (green), a component of microtubules, and DNA (deoxyribonucleic acid, pink). During prophase the nuclear envelope dissolves and the chromosomes condense. 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.