A genetic analysis of tetrahymena that have aborted normal development.

Conjugating Tetrahymena can abort the sexual cycle before the production of progeny somatic (macro-) nuclei and return to vegetative growth. We have analyzed the germinal (micronuclear) genotypes of these cells in order to determine the stage at which they aborted conjugation. Our data demonstrate that nearly all of these cells attempt meiosis, but that very few reach the successful completion of cross-fertilization. The resulting micronuclear genotypes suggest that either germinal chromosomes or entire nuclei are lost during an unsuccessful attempt at meiosis or cross-fertilization. We conclude that the decision to develop progeny macronuclei is made during meiosis and is dependent on the completion of some step necessary for successful cross-fertilization.