Biographical Memoirs Volume 69 (1996) / Chapter Skim
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TRACY MORTON SONNEBORN
TRACY MORTON SONNEBORN
Pages 268-293
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mating types in Paramecium, thereby advancing biological studies on the protozoa by a quantum leap. He clemonstratec!
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the first examples of a strange nonMenclelian phenomenon in which the macronucleus of ciliated protozoa determines the cytoplasm, and the cytoplasm in turn determines newly forming macronuclei, thereby passing genetic information from the old disintegrating macronucleus to the newly forming macronuclei. PERSONAL HISTORY i Tracy Morton Sonneborn was born on October 19, 1905' n Baltimore, MarylancI.
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Baltimore City College High School for two more years, he enterer! Johns Hopkins University with the intention of studying literature.
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then associate at Johns Hopkins. After seven years of basic studies on the life cycle of Paramecium, he made his discovery of mating types in 1937, which immediately won him fame as an investigator.
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Every task that ciaimec! his attention an experiment, a new course, a research report, a manuscript to review, a stuclent's class paper somehow became the most important thing in the woric!
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the remaining portion of Van Wagtenclonk's research career to achieve success. Early on, Ruth Dippell became his research technician.
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gave numerous prestigious lectures in this country en c! abroad.
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expect if they were clue to mutations in simple Menclelian genes. COLPIDI UM After his Ph.D.
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move from organism to organism. He stuck to his plan faithfully, studying Paramecium almost exclusively cluring his whole research career.
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normally is lost cluring subsequent fissions, while the two micronuclei undergo meiosis. A single haploic!
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the ability to make crosses between different lines. Many different mating types, characteristic of different strains of P
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in such a way that one mating type is expressed in one caryonicle, while another mating type is expressed in a sister caryonicle. Only tociay are we coming to appreciate the many cases of nuclear differentiation that occur cluring clevelopment in the metazoa.
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In short, in the formation of new macronuclei the cytoplasm determines the macronucleus for mating type, en c! once the macronucleus is cleterminec!
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Genetic analysis revealer! a series of inclepenclent genetic loci, each specific for a given serotype, with one gene active at a time.
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Perhaps in higher organisms that same was true, but it was being masked by the processes occurring in embryological clevelopment. So at this time the plasmagene theory was born: It was postulated that all genes in all organisms produce a self-reproclucing entity that persists through somatic cell divisions but that is lost cluring sexual reproduction.
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macronuclear inheritance like that observer! for certain mating types.
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THE SPECIES PROBLEM When Sonneborn discovered mating types, he found twentyeight types among different strains. He was able to show that only mating type I could mate with mating type II, only III with IV, en c!
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Sonneborn also pointed out that the sibling species of the P aurelia group, as well as the sibling species of other protozoans that are delimited primarily by their mating types, presented a set of interesting ecological and evolutionary problems.
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that it was inheritec! just as mating type was inheritec!
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Investigations of mutations and genetic fine structure also were possible. These were the studies that finally led to our knowledge of the roles of DNA and RNA and produced the modern revolution in molecular biology.
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of protozoan research. ~ HAVE DRAWN ON unpublished material in my files, much received from Tracy himself over the years, as well as unpublished material from Ruth Dippell and Ruth Sonneborn, his wife.
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23:378-85. 1939 Paramecium aurelia: mating types and groups; lethal interactions; determination and inheritance.
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LeSeur. Antigenic characters in Paramecium aurelia (variety 4~: determination, inheritance and induced mutations.
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1975 The Paramecium aurelia complex of fourteen sibling species. Trans.
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