STUDIES ON THE EXPERIMENTAL CONTROL 

 OF THE MUTATION PROCESS 



Ake Gustafsson 

 Stockholm 51, Sweden 



The work carried out by a Swedish group for theoretical and appHed 

 mutation research in plants combines radiobiological aspects, in a broad 

 sense, with radiation chemistry and genetics. A series of organisms, mostly 

 phanerogam species of agricultural character, are included in this research 

 work. The radiations range from the sparsely ionizing gamma rays of a 

 cobalt 60 source, electrons from a synchrotron or from disintegrating 

 phosphorus 32, to X-rays of varying hardness, fast and thermal neutrons, 

 as well as alpha rays and fission fragments. Recently also the effects of ultra- 

 violet, radioactive substances of different kinds and various chemical com- 

 pounds have been studied. The material treated consists either of dormant 

 or germinating seeds and pollen grains given one-time doses, or living plants 

 irradiated over the entire or part of the vegetation period. Some results of 

 this group work have recently been summarized^. 



The experiments to be reported here concern the course of the mutation 

 process, its control and intentional experimental direction. Generally said 

 mutations, whether spontaneous or induced, are detrimental in character, 

 i.e., in the homozygous condition and in an environment optimal to the 

 mother variety they decrease viability (which is here measured in an exact 

 way). In the single or heterozygous condition some mutations, however, 

 although detrimental when homozygous, increase viability. A very few, 

 say one or two of a thousand genotypical changes, are directly beneficial 

 to the organism, i.e. they augment viability both as regards vegetative 

 matter and seed production, also under conditions optimal to the mother 

 strain. 



Every organism, variety or species, has its own mode of mutating, depend- 

 ing on its genotypical constitution, chromosome number or population 

 structure. Some mutations are very rare, others more frequent ; some 

 genes are highly stable, others unstable, etc. The statistical or random 

 character of the mutation process argues against a Lamarckian interpre- 

 tation of evolution, i.e. genes do not change owing to environmental influences 

 in a direction parallel to the type of environment. This does not exclude the 

 possibility that we are able of experimentally controlling or even directing the 

 mutation process. Such a state of things was pointed out by Gustafsson^. 



The first task undertaken involved a change of the course of mutation, 

 so that its random character is obliterated. A series of papers were published 

 on this matter by Gustafsson^ and co-workers. In 1948 Gustafsson and 

 Mac key* obtained some data indicating that mutations destroying chloro- 

 phyll formation are not the same, statistically seen, after treatments with 

 mustard gas substances as with X-irradiation or spontaneously. This was 



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