Section 5 — Mutagenesis 



From 608 wild inseminated females 123 out- 

 bred strains with inbreeding of 0.26 and 124 

 sibmating strains with f =0.65 (at 6th generation) 

 were obtained. 



At the 5th generation each strain have been 

 divided in two strains each with 15 pairs of flies. 



For each strain one culture was submitted to 

 600 r of a Co 60 gamma source. 



The relatively outbred strains gave a total of 

 40,126 flies in the control (K) and 41,363 from 

 the irradiated parallel cultures (R). 



An hierarchal analysis of variance showed no 

 significant difference between treatments (F = 

 0.002, F.05 (1244) = 3.89). The same non- 

 significant result was obtained at the more 

 inbred strains in a total of 28,158 flies in the 

 control and 27,100 Fi of irradiated strains. 



A paired analysis of irradiated-control failed 

 to show any significant overall increase of the 

 irradated or the control. Considering all the 

 paired strains in which a betterment of repro- 

 ductive performance was observed after radia- 

 tion, a parcel of 51.22 per cent among 123 strains 

 and 45.16 per cent among 124 strains, contrib- 

 uted to a significant / value. 



We have indications that several strains do 

 increase performance after radiation. The aver- 

 age effect on the total population is certainly 

 counterbalanced by the others that shows a 

 significant decrease. 



produced an overall enhancement of egg-adult 

 viability; K (d) == 32.53 per cent, R(d) = 44.44 

 per cent for 10,650 eggs fertilized by control and 

 irradiated spermatozoids. Nevertheless, the sper- 

 matozoids produced from irradiated spermatides 

 and spermatocytes showed a slight decrease in a 

 total of 1 1,230 eggs, K (d) == 32.5 per cent R (d) 

 = 30.8 per cent. 



The increase of egg-adult viability among the 

 (d) level "low" class is K (d) = 7.53 per cent, 

 R (d) == 40.85 per cent, placing its average via- 

 bility over that of "high" class after radiations: 

 K (d) == 62.95 per cent, R (d) == 33.74 per cent. 

 The variance increased significantly among the 

 irradiated spermatozoid block, considering that 

 the extremes (high and low) of viability regressed 

 toward the average more among the radiated 

 than between the control the median class 

 showed the greater increase in variance. 



Our results partially support the Wallace n 

 and Wallace and Dobzhansky 2l results. Con- 

 sidering that the more commonly induced mu- 

 tations are the ones that recur most in natural 

 conditions also, and consequently, are more 

 likely to be co-adapted in balanced genie systems 

 of a race gene pool, these are probably the same 

 that improved the "low" class strains. 



1. Evolution 12, 532. 



2. Genetics 47, 1027. 



5.62. Restoration, Without Selection, of Balanced 

 Genetic Load by Radiation of Drosophila Inbred 

 Strains. A. R. Cordeiro, M. L. Reguly and 

 A. J. Centeno (Porto Alegre, Brazil). 



5.63. Persistence of Lethals in Irradiated Natural 

 Populations of Drosophila willistoni. E. K. 



Marques, H. Winge, M. Napp and C. M. P. 

 Maciel (Porto Alegre, Brazil). 



Starting with wild inseminated D. willistoni 

 from natural populations, four levels of inbreed- 

 ing were obtained: (a) outcross, about "zero 

 level" (150 strains); (b) outcross with sib mating 

 last (5th) generation, level: 0.39 (101 strains from 

 608); (c) sib mating 5 generations, level: 0.69 

 (116 strains from 608), and sib mating 41 gener- 

 ations, near level 1.0 (1 strain from 50). Signifi- 

 cantly different egg-adult viabilities were observed 

 among these series: (a): 68.5 per cent (b): 46.9 

 per cent (c): 29.7 per cent = (d): 32.5 per cent. 



Levels (b), (c) and (d) strains were sub-cultured 

 in two simultaneous and parallel series of replic- 

 ations, one (R) received 600 r from a Co 60 source, 

 the other (K) was submitted to the same conditi- 

 ons, except radiation. 



A total of 127,010 eggs have been counted in 

 these experiments. The most pertinent results are: 

 at the (b) and (c) levels the (K) did not differ 

 from (R). Nevertheless at the (d) level radiation 



An isolated wood in the grassland region of 

 R. G. Sul (Brasil) received during one year six 

 releases of about 71,000 individuals Fi of irra- 

 diated samples from a laboratory population 

 originated from the same wood. A total of 

 45,000 r from a Co 60 gamma source was delivered 

 to these six samples. The Fi of the last irradiated 

 sample, 6Ri, as well as the samples collected in 

 the isolated wood, 5 generations (N6R0 and 15 

 generations (3N6Ri) after the release of 6Ri 

 have been genetically analysed for the II and III 

 chromosomes. 



The 6Ri exhibited a significant overload of 

 lethals (II chromosome: 69.75 per cent; III chro- 

 mosome: 30.87 per cent in regard to its control 

 values from another unirradiated isolated wood 

 (II: 26.34 per cent; III: 19.02 per cent). The alle- 

 lism increased for each sample: II: 6Ri = 6.39 

 per cent and Control = 1 .02 per cent ; III : 6Ri = 

 4.00 per cent and Control = 0.29 per cent. This 



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