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The goal of the National Academies Summer Institute is to change teaching practices in introductory, undergraduate biology courses.

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The process of pair formation by sexual strains of Tetrahymena pyriformis is an inducible pathway interrupting the cellular activities of vegetative growth. A specific series of events leading from vegetatively growing cells to mating pairs is described. The sequence is composed of two separate stages: initiation and co‐stimulation. Initiation is the response to certain starvation conditions, is sensitive to tonicity, is independent of mating types, and takes about two hours at 30°C. Co‐stimulation is a reaction between already initiated cells of different mating types, requires specific cell‐cell interactions, takes about one hour at 30°C, and results in stimulated cells which are able to form pairs. An understanding of the sequence leading to the programmed developmental activities of conjugation makes possible efficient mating techniques and facilitates a search for genetic and physiological constituents of the entire pathway.