Validity of the Bunsen-Roscoe law in the production of mutations by radiation of extremely low intensity

PART - I: GENE MUTATION #1. Drosophila sperms were irradiated in the body of impregnated females with 70 milligrams of radium continuously for a period of 720 hours at two dosages of 2000 and 400r with an intensity of 1/20 and 1 /l00r per minute, respectively. #2. The frequency of the sex -linked lethals produced was found to be directly proportiona to the dosage independent of the intensity of irradiation. #3. To compare the results obtained at lower intensities, another group of impregnated females were radiated with an intensity of 4/5r per min. giving a total dosage of 2000r in 45 hours. The mutation rate was found to be independent of the duration and intensity of treatment and dependent only on the total dosage applied. PART - II: TRANSLOCATION Two lots of mature spermatozoa of Drosophila melanogaster (wild type), present in inseminated females of the bw e ey stock, were irradiated with gamma rays of radium for a period of one month (720 hours). They were given total doses of ca2000r and ca400r, at intensities of 1 /20r and 1 /100r per minute, respectively, and the frequencies of gross rearrangements (translocations) in the sperms of the two lots were determined. Two other lots of sperm were given the above total dosages at an intensity of ca4 /5r min, the period of radiation being in this case 45 hours for 2000r and 9 hours for 400r. The results obtained are :- #1. The frequency of translocations in Drosophila sperms is independent of either the intensity or the time distribution of the dosage and is dependent only on the total dosage, thus following the Bunsen- Roscoe law. #2. The data on the frequency of translocations at the two different do sages shows an exponential relationship. The frequency varies more 38. at a rate of somewhat greater than the 3/2 power of the dosage, as is expected for these low doses on the breakage theory of the formation of gross chromosome -rearrangements. #3. A comparison of the translocation frequencies obtained by Makhijani working in our laboratory with similar total dosages of X -rays (as measured both by dosimeter readings and lethal percentages) with the results of the present work shows that the frequency of translocation is independent of the wave length of radiation for the region of the spectrum extending from X -rays to gamma rays. It is also independent of the time- intensity factor, i.e. it follows the Bunsen -Roscoe law, over a time -intensity range of 10,000X. #4. The possible bearing of these findings have been discussed in relation to the treatment of cancer