Mating Type Determination 

 in Paramecium aurelia 

 A Study in Cellular Heredity * 



DAVID L. NANNEYf Indiana University, Bloomington, 

 and University of Michigan, Ann Arbor 



The genetics of Parajneciimi, in its modern sense, had its beginning 

 in the discovery of mating types in P. aurelia (Sonneborn, 1937), 

 and the determination and inheritance of mating type was the first 

 problem attacked with the newly acquired possibility of cross- 

 breeding analysis. Although many fundamental discoveries essential 

 for the understanding of this problem were made by Sonneborn 

 (1947), the determination and inheritance of mating types in this 

 species have remained less well understood than the genetics of other 

 characteristics, such as the killer and the antigenic traits (Sonneborn, 

 1950b). 



Two major difficulties have been encountered in trying to un- 

 derstand the mating type system. One of these has been to account 

 for differences among nuclei arising by mitotic divisions from a 

 common source. Another has been to account for what seemed to be 

 two very different systems of determination and inheritance of mat- 

 ing type in different races of this species. Recently (Nanney, 1953) 



* A contribution (No. 509) from the Zoology Department, Indiana Uni- 

 versity and from the University of Michigan. 



t Part of the work reported was accomplished with the aid of a Pre- 

 doctoral Research Fellowship from the National Cancer Institute, Public 

 Health Service, Federal Security Agency. The work was done in part under 

 grants to Professor T. M. Sonneborn from the American Cancer Society 

 through the Committee on Growth of the National Research Council, from 

 Indiana University, and from the Rockefeller Foundation. The work at the 

 University of Michigan has been aided by a Faculty Research Grant from 

 the Rackham School of Graduate Studies and by a grant from the National 

 Science Foundation. 



The author wishes to express his gratitude to Professor T. M. Sonneborn 

 and the entire group of Paraviecimn investigators at Indiana University for 

 their contributions in developing the ideas set forth in this paper. 



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