Section 5 — Mutagenesis 



The differences between these three groups are 

 significant. The three basal compounds did not 

 show any distinct mutagenic effect. Moreover, we 

 got differences between the mutation rates of the 

 postmeiotic stages within single groups. So A 

 proved to be more mutagenic than B, and E more 

 than F and G. All ethyleneimines also induced 

 mutations in the meiotic stages of the spermato- 

 genesis. In premeiotic stages a mutagenic efficacy 

 could be established for A, C, and D, but not for 

 E, H, and K. 



5.30. Somatic and Gonadal Mosaicism in D. melano- 

 gaster. E. A. Carlson and J. L. Southin (Los 



Angeles, U.S.A.). 



Simultaneous experiments in chemical muta- 

 genesis using the specific visible dumpy (2, 13.0) 

 and using sex-linked lethals have demonstrated 

 a considerable degree of mosaicism for both 

 approaches. The two methods are not directly 

 comparable because only gonadal tissue is as- 

 sayed in the sex-linked lethal test, while both 

 somatic and gonadal tissue may be assayed for 

 the specific visible test. The use of brood analysis 

 (postmeiotic and premeiotic sperm) for both 

 assay systems indicates a shift from postmeiotic 

 mosaically occurring mutant individudals to 

 premeiotic "complete" (non-fractional) mutant 

 individuals. This is expressed by modification of 

 the premeiotic F2:F3 sex-linked lethal frequency 

 and by the presence of both somatic and gonadal 

 complete mutation in most of the premeiotic 

 dumpy mutants. These studies have enabled us 

 to calculate the fraction of a gonad carrying the 

 mutant tissue, the number of individuals carrying 

 mosaic sex-linked lethals, and the total mutation 

 frequency for agents inducing mosaicism. A 

 theory which predicts the ratio of F2:F3 sex- 

 linked lethals from the analysis of the mutant 

 classes in a specific visible test has also been 

 inferred from the data presently available. 



Sex-linked lethal experiments have demon- 

 strated an F2 (gonadal complete) mutation fre- 

 quency of 11.3 per cent and an F3 (from F2 

 gonadal mosaic) mutation frequency of 3.8 per 

 cent. The number of F2 gonadal mosaics in the 

 total F2 females sampled is 9.21 per cent. The 

 portion of gonad containing sex-linked lethals is 

 44 per cent. It can be shown from our data that 

 the cells forming the polar cap are non-randomly 

 selected and probably do not consist of more 

 than four cells in most instances. The F2:F3 mu- 

 tation frequency for 1-4 day sperm is 1.8; for 

 5-6 days 1.1 : for 7-9 days 4.1 ; for 10-11 days 7.9; 

 for 12-14 days 24.8 and for 15-18 days 13.8. The 

 mean F2:F3 sex-linked lethal frequency for all 



broods is 3.0. These results are corrected for 

 spontaneous sex-linked lethal frequencies. The 

 mutagen used for this study is monofunctional 

 quinacrine mustard (I.C.R.-100). 



5.31. The Mutagenic Activity of Formaldehyde- 

 treated Ribonucleic Acid in Drosophila mela- 

 nogaster. Thomas Alderson (Cambridge, 

 Great Britain). 



In experiments using a chemically-defined 

 axenic treatment medium, it has been shown that 

 formaldehyde exhibits no mutagenic activity 

 towards Drosophila melanogaster larvae unless 

 ribonucleid acid is present in the treatment 

 medium. Further analysis of this phenomenon 

 has shown that adenylic acid is the active 

 component of ribonucleic acid uniquely con- 

 cerned. The presence of adenylate in the treat- 

 ment medium is apparently necessary for the 

 mediation of the mutagenic activity of formal- 

 dehyde, whether adenylate is present as the free 

 mononucleotide or bound in ribonucleic acid 

 polynucleotide. An in vitro reaction product of 

 formaldehyde with adenylate appears to be the 

 effective mutagenic alkylation. 



Since formaldehyde-induced mutagenesis has 

 not previously been attained in the absence of 

 free formaldehyde, experiments have been 

 carried out to determine whether the necessary 

 formation of alkylated-adenylate is itself a 

 sufficient condition for the mediation of the 

 mutagenic activity of formaldehyde. Ribonucleic 

 acid treated with formaldehyde under conditions 

 used in mutation tests and dialysed free of 

 unbound formaldehyde, was found to be decided- 

 ly mutagenic towards Drosophila larvae. Ribo- 

 nucleic acid similarly handled, but not treated 

 with formaldehyde, showed no mutagenic 

 activity. No difference is observed between the 

 two series in the developmental time of the 

 larvae or in the emergence of imagines. It would 

 thus appear that the in vitro alkylation of 

 adenylic acid by formaldehyde is both a neces- 

 sary and sufficient condition for the mediation 

 of the mutagenic activity of formaldehyde. 



5.32. The Elimination of a Specific Chromosome 

 Segment by Nucleic Acids in Drosophila 

 melanogaster. O. G. Fahmy and Myrtle 

 J. Fahmy (London, Great Britain). 



Macromolecules (nucleic acids, proteins and 

 ionic polymers) were shown to be mutagenic as 

 regards the induction of small chromosome 

 deletions (Minutes). Three grades of phenotypic 



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