On the effects of X-irradiation on the chromosomes of Yoshida sarcoma cells. (A preliminary report)

Abstract

The Yoshida sarcoma, a rat ascites tumor, was irradiated with X-rays at dosages of 500r, 1000r and 1500r, and the chromosomes were observed in tumor cells.
1. It was found that the chromosome-number mode of tumor cells in unirradiated tumor-bearing animals occurred at 40. The chromosomes were morphologically analysed according to the system of Tjio and Levan (1956), and the number of chromosomes assorted in three morphological groups was 13 for M, 13 for S and 14 for T.
2. Breaks and translocations of chromosomes were rather common and remarkable in metaphase cells observed in irradiated tumor-animals. It was observed in individual cells that there was no constancy in the number of M, S and T chromosomes which were unaltered by irradiation. From this result, it seems probable that there is no differential radiosensitivity by chromosomes of different types.
Two chromosomes of M type are outstanding as marker elements because of their remarkably large size. In the two marker chromosomes, the frequency distribution of breakage was observed after irradiation, and showed that the breakage was rather frequent on both arms around positions one-fourth distant from the centromere.