Section 5 — Mutagenesis 



increase persisted five generations in nature: 

 N6R1: II = 3.82 per cent; III = 3.22 per cent. 

 This high allelic frequency was maintained in spite 

 of the return to control values of the III chro- 

 mosome lethals. The II chromosome lethal 

 frequency was still significantly higher than the 

 control (44.44 per cent). The allelism tests inter- 

 samples (6R1 N6R1 : II = 5. 1 8 per cent ; III = 

 3.03 per cent and 6R1 :< Control: II == 0.22 per 

 cent; III = 0.07 per cent allowed us to estimate 

 the radiation induced lethal persistence at the 

 N6R1 to be 75.82 per cent for the II and 89.51 per 

 cent for the III chromosome. 



The same type of calculations made for the 

 3N6Ri gave 1 1 .48 per cent for the II and 5.30 per 

 cent for the III chromosome, as values of lethal 

 persistence from the 6R1, 15 generations after 

 under natural selection. There are indications that 

 several components of the adaptive value were 

 depressed ( l ) and that chromosomal inversions 

 might "protect" some lethals ( 2 ). The persistence 

 of some lethals suggests their complete recessivity 

 as even some balanced effects. 



1. Marques and Maciel, Experientia 17, 404. 

 1961. 



2. Cordeiro, Experientia 17, 405, 1961. 



6.64. Genetic Effects of y-Irradiation on the Percent 

 Adult Emergence of Drosophila melanogaster. 

 J. C. DeFries and R. W. Touchberry (Ur- 

 bana, U.S.A.). 



Newly emerged males and females from two 

 populations (randombred and inbred) derived 

 from Luce's wild type strain were subjected to 

 various dosages of y-irradiation (0, 500, 1000 or 

 1500r) and mated in all possible combinations 

 within populations, resulting in a four X four 

 factorial arrangement of treatments. Three mat- 

 ing pairs were included in each subclass of two 

 replicate experiments, requiring a total of 96 

 mating pairs per generation in each experiment. 

 Eggs were collected over a 10-day period follow- 

 ing treatment and the percent of the offspring to 

 emerge as adults was determined. In addition to 

 these data of generation one (offspring of treated 

 flies), similar data were obtained for generations 

 two and three, resulting from full-sib matings of 

 generations one and two, respectively. Somatic 

 and genetic effects would be expressed in gener- 

 ation one, whereas only genetic effects would be 

 expressed in subsequent generations. 



Highly significant linear depressing effects 

 resulting from treatment of both males and 

 females were observed in the data of generation 



one, with the magnitude of the effect being greater 

 for males than females. Highly significant effects 

 resulting from treatment of the original males, 

 although smaller in magnitude than in the first 

 generation, were again found in the data of 

 generations two and three; however, no effect 

 was evident from treatment of the original fe- 

 males in these later generations. 



This investigation was supported in part by 

 Research grant GM-07951-03 from the Public 

 Health Service. 



5.65. The Sex Ratio in the Offspring of Irradiated 

 Avian Males. M. Vojtiskova, V. Matousek 

 and A. Lengerova (Prague, Czechoslovakia). 



Birds proved to be advantageous material for 

 studying the radiation effect on the sex ratioin 

 the offspring of irradiated homogametic and non- 

 irradiated heterogametic parents, since 



(a) they can be bred in large numbers under 

 standard conditions; 



(b) in contrast to mammals, the homogametic 

 sex in avian species is male; this circumstance 

 makes it possible to extend the followup of the 

 dose-effect relationship to a higher dose range, 

 since the sterilizing dose for males is much higher 

 than for females. In addition, each irradiated 

 individual has a large number of offspring, which 

 is very useful from the aspect of the requirements 

 of statistical analysis. 



In the present experiment a total number of 

 1 1,874 birds was used to estimate the shift in the 

 sex ratio after the X-ray irradiation of males. 

 Within the dose range 0-600 r the shift was found 

 to lie between the limits of 1 10" 5 to 8 10~ 5 

 per 1 r of irradiation with a confidence coefficient 

 of 0.95. 



5.66. Influence of Fast Neutrons on Frequency of 

 Lethal Mutations in the Reproductive Cells of 

 Male Mice. M. D. Pomerantzeva (Moscow, 

 U.S.S.R.). 



The males of white mice were totally irradiated 

 by fast neutrons (with average energy ~ lMeV) 

 in the horizontal canal of a nuclear reactor. The 

 average dose rate of fast neutrons was 350 rad/hr, 

 the concomitant dose of y-rays was 85 rad/hr. 

 The following doses of fast neutrons were used: 

 17. 34, 57, 114, 171 and 228 rad. Immediately 

 after irradiation and on the 18th day after irra- 

 diation each male was kept for 3 days with 2 to 



77 



