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Title: Genetic analysis of a Myxomycete
Author: Dee, Jennifer
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1961
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The work was undertaken because genetic analysis of Myxomycetes may eventually yield information about the action of genes in morphogenesis. The Myxomycetes are among the simplest organisms in which morphogenesis occurs and in which the effects of genes in different cellular environments may be studied. No previous work on genetics of Myxomycetes has been reported. The species used was Physarum polycephalum, which had previously been described but had never been cultured through its life-cycle under controlled conditions. The plasmodium, an amorphous syncytium, grows vegetatively or ceases growth and produces spores. The spores release uninucleate "amoebae" which divide repeatedly. An unknown number of amoebae fuses to form a plasmodium. An the present work, techniques were developed by which each one of these four phases of the life-cycle could be produced when required and in the presence of only one other organism as food, a strain of Pseudomonas fluorescens. Some of the processes underlying the life-cycle were elucidated. B3s;periroents showed that amoebae cultured from a single spore would not form a plasmodium, that plasmodia were formed only by certain combinations of amoebae from different single-spore cultures, and that these combinations indicated the existence of two mating-types among the cultures investigated. Photometric measurements of desoxyribonucleic acid (DNA) content of nuclei in plasmodia and amoebae were done to determine the relative ploidy of the nuclei in these two stages, but the results were inconclusive. A plating method for amoebae (or spores) was developed to provide a moans of accurate quantitative estimation of growth, the isolation of rare mutants and the isolation of large numbers of progeny from crosses. One clone of amoebae resistant to emetine hydrochloride was isolated. A plasmodium synthesised from this mutant clone and a sensitive clone of opposite mating-type was found to be sensitive to emetine. Three hundred clones of amoebae, each obtained from single spores produced by this "hybrid" plasmodium, were tested for emetine-resistance and mating-type and, with respect to these factors, both parental and both recombinant types were found. The frequencies of the four types indicated that emetine-resistance and mating-type are determined by pairs of alleles at two unlinked genetic loci. These results show that genetic recombination occurs during the life-cycle of this Myxomycete and that genetic analysis of the organism is therefore possible.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available