Mutants of sexual maturity in Paramecium caudatum selected by erythromycin resistance.

Cells of Paramecium caudatum, syngen 3 usually become sexually mature about 50 fissions after conjugation. In order to study the genetic mechanisms that control fission-department expression of maturity, an attempt was made to obtain early mature mutants by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. A new cytoplasmic marker, erythromycin resistance, was used to eliminate nonconjugant and macronuclear regeneration clones. Twenty early mature clones were obtained from five different mutagenized cultures. Three of them were genetically analyzed by crosses to wild-type stocks. The results show all three mutants to be controlled by incompletely dominant genes, i.e., the homozygotes became mature 20-25 fissions and the heterozygotes 15 fissions earlier than the wild-type clones. At least two different loci are suggested for the early maturity.