The cytokinesis-block micronucleus cytome assay (CBMN Cyt) is a comprehensive method for assessing DNA damage, cytostasis, and cytotoxicity. It specifically scores micronuclei (MNi), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) in once-divided binucleated (BN) cells. MNi are biomarkers of chromosome breakage or loss, NPBs indicate DNA misrepair or telomere end-fusions, and NBUDs reflect gene amplification or DNA repair complex elimination. Cytostatic effects are measured by the proportion of mono-, bi- and multinucleated cells, while cytotoxicity is assessed via necrotic and apoptotic cell ratios. The assay is used for biomonitoring genotoxic exposure, in vitro testing, and research in nutrigenomics and pharmacogenomics. It also predicts radiation sensitivity and cancer risk. The CBMN Cyt assay is reliable and reproducible, making it a standard cytogenetic test for genetic toxicology. It has evolved into a comprehensive method for measuring chromosome breakage, DNA misrepair, chromosome loss, non-disjunction, necrosis, apoptosis, and cytostasis. It also measures NPBs and NBUDs, which are biomarkers of chromosome rearrangement and gene amplification, respectively. The "cytome" concept implies scoring all cells for viability, mitotic status, and chromosomal damage. This technique is now referred to as the cytokinesis-block MN cytome (CBMN Cyt) assay. NPBs are scored in the CBMN Cyt assay because they provide evidence of chromosome rearrangement, which is not achievable if only MNi are scored. NPBs occur when centromeres of dicentric chromosomes are pulled to opposite poles during anaphase. They can be observed in BN cells due to cytokinesis inhibition. NPBs are formed by misrepair of DNA breaks or telomere end-fusions. They are also observed in models of rodent and human intestinal cancer and correlate with telomere length. Nuclear budding is a unique mechanism of MNi formation, observed under conditions of gene amplification or folic acid deficiency. Amplified DNA is eliminated via nuclear budding to form MNi during S phase. NBUDs are characterized by a narrow or wide stalk of nucleoplasmic material connecting them to the nucleus. The duration of the budding process and the extrusion of MNi are not well understood. Folic acid deficiency has been shown to correlate with MNi, NPBs, and NBUDs. These markers are significantly reduced at 60–120 nM folic acid. A strong cross-correlation between MN, NPB, and NBUD frequencies suggests a common mechanism initiated by folic acid deficiency-induced DNA breaks, likely involving chromosomal instability. MNi can also be a surrogate marker for DNA hypomethylationThe cytokinesis-block micronucleus cytome assay (CBMN Cyt) is a comprehensive method for assessing DNA damage, cytostasis, and cytotoxicity. It specifically scores micronuclei (MNi), nucleoplasmic bridges (NPBs), and nuclear buds (NBUDs) in once-divided binucleated (BN) cells. MNi are biomarkers of chromosome breakage or loss, NPBs indicate DNA misrepair or telomere end-fusions, and NBUDs reflect gene amplification or DNA repair complex elimination. Cytostatic effects are measured by the proportion of mono-, bi- and multinucleated cells, while cytotoxicity is assessed via necrotic and apoptotic cell ratios. The assay is used for biomonitoring genotoxic exposure, in vitro testing, and research in nutrigenomics and pharmacogenomics. It also predicts radiation sensitivity and cancer risk. The CBMN Cyt assay is reliable and reproducible, making it a standard cytogenetic test for genetic toxicology. It has evolved into a comprehensive method for measuring chromosome breakage, DNA misrepair, chromosome loss, non-disjunction, necrosis, apoptosis, and cytostasis. It also measures NPBs and NBUDs, which are biomarkers of chromosome rearrangement and gene amplification, respectively. The "cytome" concept implies scoring all cells for viability, mitotic status, and chromosomal damage. This technique is now referred to as the cytokinesis-block MN cytome (CBMN Cyt) assay. NPBs are scored in the CBMN Cyt assay because they provide evidence of chromosome rearrangement, which is not achievable if only MNi are scored. NPBs occur when centromeres of dicentric chromosomes are pulled to opposite poles during anaphase. They can be observed in BN cells due to cytokinesis inhibition. NPBs are formed by misrepair of DNA breaks or telomere end-fusions. They are also observed in models of rodent and human intestinal cancer and correlate with telomere length. Nuclear budding is a unique mechanism of MNi formation, observed under conditions of gene amplification or folic acid deficiency. Amplified DNA is eliminated via nuclear budding to form MNi during S phase. NBUDs are characterized by a narrow or wide stalk of nucleoplasmic material connecting them to the nucleus. The duration of the budding process and the extrusion of MNi are not well understood. Folic acid deficiency has been shown to correlate with MNi, NPBs, and NBUDs. These markers are significantly reduced at 60–120 nM folic acid. A strong cross-correlation between MN, NPB, and NBUD frequencies suggests a common mechanism initiated by folic acid deficiency-induced DNA breaks, likely involving chromosomal instability. MNi can also be a surrogate marker for DNA hypomethylation