CYTOGAMY: AN INDUCIBLE, ALTERNATE PATHWAY OF CONJUGATION IN TETRAHYMENA THERMOPHILA

Eduardo Orias ¹ and Eileen P. Hamilton ¹

¹ Section of Biochemistry and Molecular Biology, Department of Biological Sciences, University of California at Santa Barbara, Santa Barbara, California 93106

We report the occurrence of cytogamy in Tetrahymena thermophila. By analogy to Paramecium, cytogamy generates exconjugant clones that derive their entire genetic information from a single meiotic product of their cytoplasmic parent. Thus, "instant" whole-genome homozygotes are created. Cytogamy has been induced in every strain of T. thermophila tested, and most of the excytogamous progeny have exhibited high fertility. The high frequency with which cytogamy can be induced by hyperosmotic shock, coupled with the foregoing genetic properties, make this process a practical (and already proven) method for the isolation of recessive mutants in T. thermophila. We also report that the cytogamy-inducing treatment induces other rare abnormalities of genetic transmission, which have not yet been characterized.

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