Nearly all methods of chromosome banding rely on
harvesting chromosomes in mitosis. This is usually
achieved by treating cells with tubulin inhibitors, such as
colchicine or demecolcine (colcemid), that depolymerize
the mitotic spindle and so arrest the cell at this stage.
Excessively long incubations with Colcemid result in
overcondensed chromosomes that band poorly and moreover some cell types, especially those from the mouse,
eventually escape the Colcemid block and proceed through
the cell cycle.