 Later, the cytokinesis-block micronucleus (CBMN) method was established, where Cyt-B, an inhibitor of the spindle assembly, was used to prevent cytokinesis occurring after nuclear division.The CBMN method is used for the assessment of chromosomal loss, breakage, and associated apoptosis and necrosis induced by different mutagens.A micronucleus is the erratic (third) nucleus that is formed during the anaphase of mitosis or meiosis.