Section 10 — Developmental Genetics 



suppressor (su-tu). This second tu gene was 

 fully penetrant and not an allele of the first. 

 Despite these genetic differences, both strains 

 responded by an increase of tumour penetrance 

 to (a) a sub-optimal balance of dietary pentose 

 nucleotides, (b) cholesterol deficiency and (c) 

 excess 1-tryptophan. Their Fi responded simi- 

 larly to these abnormal conditions. Only the 

 homozygous tu; su-tu strain reacted with a 

 high tumour frequency to X-irradiation of 

 embryos, suggesting that X-rays affect only the 

 su-tu system. 



10.27. Genes, Amino and Nucleic Acids, Progressive 

 Tissues and Cancer. Investigations on Poeciliid 

 Fish, Nicotiana, Drosophila and Vitis. F. 



Anders, A. Anders, F. Drawert and E. 

 Steitz (Geilweilerhof/Pfalz, Germany). 



Platypoecilus maculatus has a gene causing 

 black spots on its body-surface (Gordon, 

 Kosswig). These spots represent a "progressive 

 tissue" (Anders et al., Experientia 1963, in 

 press), because they enlarge in a positive allo- 

 metric manner, while the number of their con- 

 stituents, macromelanophores, increases. P. 

 maculatus has a low level of free amino acids. In 

 contrast, Xiphophorus helleri lacking this gene 

 has a high one. Certain hybrids of these species 

 show a high amino acid level, and, when car- 

 rying the spot-gene from P. maculatus, exhibit 

 an abnormal increase in the number of macro- 

 melanophores thereby producing melanomas. 

 Whether or not tumour formation takes place 

 seems to depend on presence or absence of 

 macromelanophores and on amino acid level. 

 Hybrids of 8 other poeciliid species and sub- 

 species have shown the same dependence. 



In certain hybrids of Nicotiana producing ge- 

 neticaltumours, a similar correlation is found. 

 On the basis of this analogy, N. glauca for instance 

 may be compared to P. maculatus and N. langs- 

 dorffii to X. helleri. In Drosophila melanogaster a 

 correlation between amino acid level and tu- 

 mour formation exists too. In Vitis it was found 

 that injection of certain amino acids causes 

 neoplasms identical with galls of Phylloxera, 

 when meristematic ( = progressive) tissues are 

 present. 



Further investigations have shown that high 

 concentrations of free amino acids may accelerate 

 biosynthesis of RNA and that autonomous growth 

 of tumour may be caused by a high level of 

 RNA. A simple genetic concept for cancer for- 

 mation will be discussed. 



10.28. Induced Mutations in Barley causing Trans- 

 formation of Lodicules. O. P. Kamra (Halifax, 

 Canada). 



During induced mutation experiments in 

 barley, using X-rays, Y-rays, neutrons and 

 chemicals, several single gene mutants with al- 

 tered sex organs were isolated. In these mutants 

 changes in the structure and function of the 

 lodicules were observed. 



In the mutants 1 to 4 lodicules are produced. 

 The normal barley spikelet has two lodicules. 

 The extent of transformation varied greatly from 

 a slight modification in shape and structure to 

 complete alteration in form and function. The 

 two lodicules may fuse to form one highly vas- 

 cular lodicule or may be transformed into func- 

 tional pistils or stamens. 



The lodicules are considered to have evolved 

 from the petals. From detailed histological and 

 cytogenetical investigation of these mutants a bet- 

 ter understanding of gene action in differentia- 

 tion of sex organs in higher plants, and of some 

 aspects of the evolution of these organs may be 

 expected. 



10.29. Flowerstriping in Cyclamen persicum cv. 

 "Harlekin". Friedrich Bergann (Pots- 

 dam-Babelsberg, Germany). 



Self-pollinated individuals of the striped- 

 flowering Cyclamen persicum cv. "'Harlekin" do 

 not breed true. Only a certain part of the off- 

 spring is striped-flowering, the rest self-coloured 

 red or pink. The numerical proportionsvary. If 

 a "Harlekin"-bulb is decapitated, the lower 

 part of it will survive and produce numerous 

 adventitious buds from the wound. In the follow- 

 ing year most decapitated plants are flowering 

 unicolored, generally with red petioles, more 

 seldom with pink petioles. Occasionally red, 

 pink and striped flowers are found in coexist- 

 ence on the same plant. It may be concluded, 

 therefore, that flowerstriping in "Harlekin" 

 is not due to a gene but to chimerical constitu- 

 tion. 



If we suppose the shoot-apices of "Harlekin" 

 to have periclinal constitution (pink over red, or 

 red over pink), flowerstriping can be interpreted 

 as originating by tissue-rearrangements, namely 

 perforations in L 1, or partial replacements of 

 L 1 by L 2. 



Considering the evidence on "Harlekin's" 

 chimerical nature, somatic segregations and tis- 

 sue-rearrangements must be concluded to have 

 taken place in the early ontogenesis and to have 

 consequently produced mosaicism within the 



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