Confocal light micrograph of aberrant mitosis in cultured cells from mouse breast cancer tumour tissue. 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. Here, three mitotic spindles (red) have formed rather than the normal two. The chromosomes (blue) are arranged in a Y-shape rather than across the centre of the cell. During mitosis the identical chromatids that make up each chromosome are usually separated to opposite ends of the cell, pulled apart by the mitotic spindle. Three spindles will result in missegregation of the chromosomes.