Section 5 — Mutagenesis 



It has been shown by various authors that in- 

 sect embryos developing from irradiated gametes 

 can die at different stages of development. In 

 Habrobracon and Drosophila different lethal 

 syndromes seem to result from different kinds of 

 nuclear damage as shown by Von Borstel (1961). 



Different lethal syndromes can also be distin- 

 guished after irradiation of \r\sem\naXtdDrosophila 

 eggs. The dependence of the relative frequencies 

 of different syndromes after irradiation in specific 

 stages of nuclear divisions and the dose depend- 

 ence of the different syndromes have been re- 

 corded. The results indicate that radiation induced 

 genetic effects alone can hardly explain all the 

 facts. 



5.49. The Restitution of Radiation Induced Breaks 

 in Structural Heterozygotes of Diosophila. 



E. Goldschmidt, E. Barak, N. Bernstein and 

 R. Falk (Jerusalem, Israel). 



Males of Drosophila melanogaster carrying the 

 Cy (II L) inversion and their structurally homo- 

 zygous brothers were given an X-ray dose of 

 5000 r. The salivary glands were scanned in 

 larval offspring of both groups of males, and all 

 breaks induced in euchromatic sections of the 

 entire chromosome set were located. The rate of 

 induced aberrations was higher in the Fi pro- 

 duced by Cy fathers. 



The hatchability of eggs fertilized by irradiated 

 males of both groups was studied in order to 

 compare the brood patterns and the overall rates 

 of "dominant lethals" induced during the pre- 

 meiotic stages up to the first meiotic anaphase. 



It has been suggested that the loop configu- 

 ration in the heterozygous bivalent facilitates 

 non-homologous contact and thus promotes 

 abnormal restitution. A more comprehensive 

 hypothesis proposes that each of two perfectly 

 synapsed homologues provides a "splint" for the 

 normal restitution of its partner. Hence asynapsis 

 per se will interfere with the normal repair of 

 breaks. On this assumption the structural heter- 

 ozygosity of one bivalent, promoting asynapsis 

 in non-homologous elements, may be responsible 

 for the increased production of abnormal resti- 

 tutions in the entire chromosome set. 



5.50. Recessive Lethals in the IV Chromosome of 

 Drosophila melanogaster. H. J. Belitz (Berlin, 

 Germany). 



After X-ray treatment of ey 2 /ey 2 males of 

 Drosophila melanogaster with doses of 3, 4.5 and 



6 kr respectively 30 chromosomes with recessive 

 lethals and 1 1 with semilethals were found. In 

 allelic tests these 41 mutated chromosomes were 

 outcrossed with each other. Two chromosomes 

 contained two lethals each. Among the 43 mu- 

 tations no more than 25 occupy one locus; the 

 others are small deficiencies: 12 at least comprise 

 two loci, 4 each three loci, and 2 four and sixteen 

 respectively. By aid of these overlapping defi- 

 ciencies a part of this chromosome could be 

 mapped over a range of about 20 loci including 

 the locus of ci. Among the induced lethals two 

 clusters were found : one consisted of 5 mutations 

 induced in a spermatogonium and occupying 

 probably one locus; the other was composed of 

 two lethals, which gave a positive result in the 

 allelic test, but proved to be overlapping small 

 deficiences including the locus of ci. 



5.51. Crossing-over in Males of Dorsophila Induced 

 by Radio Frequency Treatment. George 

 H. Mickey (Ridgefield U.S.A.). 



Although crossing over normally does not 

 occur in the male germ cells of Drosophila, reports 

 in the literature indicate that this phenomenon 

 has been induced by treatment of male flies with 

 high temperature, X-rays, gamma-rays, ultra- 

 violet rays, formaldehyde and nitrogen mustard. 

 Our experiments yielded significant numbers of 

 recombinants in the progeny of heterozygous 

 (3ple) male flies treated with radio frequency of 

 20 megacycles. Recombinants frequently oc- 

 curred in clusters and usually without comple- 

 mentary classes. The distribution of exchange 

 regions was nonrandom. The induced crossovers 

 appear to have occurred in spermatogonial cells 

 rather than in spermatocytes. 



5.52. Different Types of Mortality Including Prolon- 

 gation of Female Lifetime after X-raying 

 Drosophila melanogaster Imagines. H. Nothel 

 (Berlin, Germany). 



The influence of X-rays on the lifespan of 

 Drosophila melanogaster imagoes has been 

 studied by application of 17 different doses 

 (100 KV, 0-125 kr) to 1-2 days old males and 

 females of the Berlin wild stock. 



A prolongation of female lifespan is induced by 

 doses >4 kr, it culminates at 11 kr in 150 per 

 cent of the mean survival time of unirradiated 

 females. The prolongation is not accompanied 

 by alterations in locomotion or copulation of 

 the females concerned and is independent from 



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