Chromosome balance and the control of malignancy

The Giemsa banding pattern of the chromosomes has been analyzed in a line of transformed golden hamster cells, revertant and re‐revertant cells and their tumors. The transformed and re‐revertant cells were malignant in vivo and had gained an additional chromosome 5 7 . Revertants with a suppression of malignancy lost this additional chromosome 5 7 and gained an additional chromosome 7 2 . The tumors produced by segregants from the revertant cells were malignant, although to a lower degree than transformed and re‐revertant cells. These tumors had lost the additional chromosome 7 2 found in revertants and gained one or two 5 12 chromosomes. The results support the hypothesis that the balance between genes for expression and suppression controls malignancy. The data indicate that chromosome 7 2 carries genes for suppression and that chromosomes 5 7 and 5 12 carry genes for expression of malignancy. The genes on chromosome 5 7 seem to result in a greater degree of expression than the genes on chromosome 5 12 . The chromosome balance that controlled malignancy in these cells, also controlled the expression and suppression of transformed properties in vitro.