Non-Mendelian Inheritance of Early Maturity in Euplotes crassus

ABSTRACT. This paper reports on a new phenomenon in the ciliated protists: cytoplasmically determined early sexual maturity. Stock MN1 of the marine hypotrich Euplotes crassus matures immediately after conjugation. We analyzed the respective contribuboas of the nucleus and the cytoplasm to the inheritance of this stable condition. A genetic marker, and new methods in E. crassus for cytoplasmic labeling, production of amicronucleates, and induction of selfing were used. Crosses within and among the early mature (EM) variants and late mature (LM) "wild type" lines were done in ovarious combinations. Descendants of EM conjugants continued to be EM, and descendants of LM continued to be LM, regardless of the different experimental approaches used. The results of the crosses clearly show that the clonally stable, variant EM phenotype is transmitted at conjugation in a non-Mendelian manner through the cytoplasmic lineage. The expression of the trait is independent of the micronuclear genome, but the precise site and nature of the hereditary basis is unknown.