Fluorescent light micrograph of cells during 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. Centrosomes appear as bright yellow dots. At left the cell is in prophase, the nuclear envelope dissolves and the chromosomes condense. The cell at centre is in metaphase, with the chromosomes aligned along the centre of the cell. The sister chromatids of each chromosome are pulled to opposite poles during anaphase (right). The chromatids are pulled apart by the mitotic spindle, the main component of which are microtubules. Each mitotic spindle emerges from a centrosome.