X-ray-induced chromosome aberrations in the leukocytes of mouse and man

In our earlier studies we showed that the frequency of dicentrics induced by x-rays in human leukocytes was about twice that induced in mouse leukocytes. The frequencies of deletions were similar in both species. However, the mouse cultures were fixed at 60 hrs and the human cultures at 54 hrs. In both cases it was likely that some of the cells analyzed were in their second post-treatment mitosis. Further studies were carried out using fixation times of 48 hrs for both human and mouse cultures. The same relationships held here, namely twice as many dicentrics in human, and similar deletion frequencies in both. The aberration frequencies observed were corrected to take account of second division cells, by assuming cells containing a dicentric without an accompanying fragment were in their second division. There were more such cells with the mouse. To further increase reliance on the conclusions, cultures were fixed at the earliest times that 300 cells per dose could be obtained--36 hrs for the mouse, 42 hrs for human. The frequencies of dicentrics were increased in both, and a relationship of about 2:1 for human to mouse was obtained. Deletion frequencies were similar in both. Three different human donors were used. Since no dicentrics without fragments were obtained, it appeared that aberration frequencies in first division cells only were being compared