Abstract
Frequent production of RD segregants was observed in the asci of tetraploid bakers' yeasts. With the intention of elucidating this phenomenon, genetic analysis was attempted. It was demonstrated that the respiration of the given bakers' yeasts is controlled by at least three complementary genes (tentatively denoted as R1/r1, R2/r2 and R3/r3). Heterozygous conditions containing many recessive alleles and segregation of them may account for the peculiar phenomenon in question. RD yeasts due to mutation of each of these respiratory genes were found to be characterized by a loss or instability of the cytoplasmic factor necessary for respiration. In other words, it was confirmed that the presence of the cytoplasmic factor in the yeasts concerned is stable by the existence of dominant genes, R1, R2 (indispensable) and R3.
