Scheme of an assay for measuring chromosome instability (CIN) based on the use of HAC containing the EGFP transgene. Cells that inherit the HAC display green fluorescence, while cells that lack it do not. It is expected that the control untreated cells should show uniform green fluorescence, while those that have lost HAC after drug treatment should be highly variable in fluorescence. Therefore, the actual number of cells with the EGFP-HAC can be measured by FACS. Thus, the compounds, which increase HAC loss and therefore increase spontaneous chromosome mis-segregation rates, may be identified.