For karyotyping, the dividing cells are arrested by the addition of colchicines in the following mitotic phase

b. Metaphase(Ref: Nelson's 20/e p 605-606, Ghai 8/e p 645)Chromosomes are examined after arresting dividing cells in metaphase with mitotic spindle inhibitors (e.g., N-diacetyl- N-methylcolchicine), followed by staining.