Metaphase cell division. Colour transmission electron micrograph (TEM) of a section through a HeLa cell during metaphase cell division (mitosis). At centre are chromosomes (orange); during metaphase the chromosomes line up in one plane in the centre of the cell, in preparation for nuclear division. The chromosomes are moved by spindle microtubules, fine straight lines forming two triangular shapes here (at top and bottom). During mitosis a cell produces two genetically identical daughter cells. HeLa cells are human cancer cells cultured in the laboratory and used in cancer research. Magnification: x4,800 at 6x4.5cm size.