Genetic Effects of X-Rays and Cathode Rays on Oocytes of Habrobracon.

IFFERENCES in sensitivity of oocytes to X-irradiation depending upon stage in meiosis when treatment occurred, have been shown for a number of organisms including Habrobracon (WHITING l938,1941,1945a, 1945b; ATWOOD, VON BORSTEL and WHITING 1956). Studies have also shown that death of Habrobracon embryos following irradiation of oocytes in late metaphase and in late prophase (diplotene) was attributable to chromosomal and not to cytoplasmic injury except fdr the highest doses applied to the late prophase oocytes (WHITING 1946, 1948, 1949, 1950, 1955). Differences in sensitivity of metaphase and prophase eggs have been shown to be great. WHITING’S data indicate that about 400r is sufficient to kill roughly 50 percent of the embryos when oocytes have been treated in metaphase, but that about 12,000r is necessary if the X-rays are delivered to oocytes during late diplotene. The author’s data have essentially confirmed these findings for metaphase oocytes (HEIDENTHAL, C ARK and GOWEN 1955). Both authors have demonstrated that X-rays induce both dominant and recessive lethals in metaphase oocytes (HEIDENTHAL 1952,1953; WHITING 1954; ATWOOD, VON BORSTEL and WHITING 1956). In addition to the comparisons of sensitivity with respect to stage, the author’s interest has involved comparisons related to differences in dose rate. In a previous paper it has been shown that there is no difference in certain genetic effects produced by 124 kv and 50 Mev X-rays (HEIDENTHAL, C ARK and GOWEN 1955). It appears that the different methods by which the ionizations are produced are not important in this biological system. In these experiments the dose rates differed by a factor of about five. In the present paper this work has been extended to include the effect of 800 kv (peak) electrons. In view of the results with 124 kv and 50 Mev similar effects might be expected (for equal dose and rate of accumulation of dose) if high energy cathode rays were used. However, on account of the higher dose rates associated with electron irradiation, differences in the genetic effect might be expected, provided the chemical reaction (or series of reactions) leading to the genetic change is sensitive to concentrations of radiation-produced active entities, e.g. free radicals.