Mating types and mating-inducing factors (gamones) in the ciliateEuplotes patellasyngen 2

SUMMARY Relationships between mating type genes and mating-inducing factors (gamones) were investigated in the ciliate Euplotes patella syngen 2. Ten mating types were distinguished, and genetic data indicated that the ten mating types were determined by four codominant alleles in possible combinations of two of them. There were six heterozygous types ( mt1 / mt2 , mt3 / mt4 , etc.) and four homozygous types ( mt1 / mt1 , mt2 / mt2 , etc.). Conjugation-conditioned fluid (CCF) obtained from a mixture of cells of homozygous types could induce homotypic pair formation in cells of all mating types except for a particular type. Genetic data of cell-CCF combination experiments suggest that each mating type allele controls the production of a specific gamone which induces pair formation in cells which do not produce the same gamone. Gamones and their hypothetical receptors are discussed.