Conditions for Mating and Inheritance of Mating Type in Variety Seven of <i>Tetrahymena pyriformis</i>*

Abstract

Induction of conjugation in clones of variety 7 of Tetrahymena pyriformis required more precise control than was necessary for the classical variety 1 clones, WH‐6 and WH‐14. Axenic methods are herein described which were successful in eliciting the mating response; especially important was a period of growth under optimal nutritional conditions, and use of animals in the logarithmic phase of growth. Three cases of presumptive age‐induced selfing are reported, along with the discovery of new mating types III and IV. The isolation of a stage intermediate between a “pure” marine type and a selfing condition offers additional evidence for mating type instability. An analysis of the system of mating‐type inheritance shows a pattern similar to that seen in Paramecium aurelia (Group B), and variety 9 of Tetrahymena pyriformis .