Non‐random distribution of abnormal mitoses in heteroploid cell lines

We have performed absorption‐cytometric DNA measurements of the DNA contents of the G₀/G₁, G₂, metaphase, and telophase cells of the heteroploid MCa‐11 and HL‐60 lines, as well as the WCHE‐5 line which has a narrowly restricted number of chromosomes. We found that morphologically unbalanced mitoses occurred much more frequently in telophase‐cell pairs of the heteroploid MCa‐11 and HL‐60 lines than in those of the chromosomally stable WCHE‐5 line. Furthermore, the morphologically unbalanced mitoses represented unequal segregation of DNA into each of the daughter telophase nuclei. Such mitotic segregation errors (MSE) occurred almost exclusively in telophase cells with DNA contents which were above, or below, the DNA content of the modal telophase population. The net effect of these non‐random, unbalanced divisions of heteroploid cells with non‐modal DNA contents is to produce one daughter cell with a DNA content that tends to return to the modal DNA content peak.