In traditional cytogenetics laboratories, cultured cells from blood and amniotic fluids are harvested so that many cells will be in "metaphase." Metaphase is a phase of the cell cycle in which the chromosomes are lined up on the metaphase plate just before segregating into daughter cells. Cells are treated with inhibitors, such as colchicine, to stop division. This is followed by a hypotonic solution, such as 0.075 M potassium chloride (KCl). The cells are then ready to be "dropped" onto a slide, rupturing the cells and resulting in metaphase spreading across the slide. The metaphase slide can then be assayed with any FISH probe.
