Epigenetic Factors Affecting Mating Type Expression in Certain Ciliates1

Excerpt

Since their discovery over twenty years ago (Sonneborn, 1937), the mating types of ciliates have continued to raise a variety of questions about the nature and mode of operation of genetic mechanisms. These problems are yet far from complete solution, but a discussion of their present status may be helpful in clarifying certain problems in genetic physiology, or at least in identifying some areas of possible confusion. The phenomena I wish to discuss occur in the genetic species (varieties or syngens) of the Paramecium aurelia-multimicronucleatum complex, of the P. bursaria complex and of the Tetrahymena pyriformis complex (Sonneborn, 1957). Each of these thirty or more species has features all its own. Although all species have not been equally well studied, the accumulated information now available is much too extensive for a detailed summary. Since a broad but superficial survey would not well serve the purposes of this symposium, I will...