Immortalized Cell Lines: Chromosome Preparation and Banding

The principle of producing mitotic chromosome preparations for analysis by banding techniques and by in situ hybridization is to synchronize the cells by blocking them at cell cycle stages preceding mitosis (Gl or S phase), then releasing the block, and allowing the maximum number of cells to reach the desired stage of mitosis, where the cell is again halted by use of mitotic poisons, usually colcemid, which arrest cells in metaphase by blocking cytokinesis. Clearly, the timing of these stages is cell-type dependent, and therefore a matter for trial and error, once the main principles of the process are understood. The timing of addition of colcemid and the duration of exposure to colcemid will also influence the length of the chromosomes obtained.