Corticotype Transmission in Tetrahymena

ECENT studies on the inheritance of cortical variations in Paramecium aurelia (SONNEBORN 1963;BEISSON and SONNEBORN 1965) demonstrate a "maternal" mode of transmission for these traits.Certain kinds of cortical variations, and particularly those observed in duplex cells or associated with inverted ciliary rows, are capable of indefinite persistence in vegetative propagation.When crosses are carried out between clones of distinctive form, the exconjugants characteristically produce clones with the original patterns of organization, even though they have become genically equivalent.Even when the solated cytoplasm is massively exchanged during conjugation, the exconjugants retain their peculiarities.These observations, with others, virtually exclude any possibility that differences in either the primary structure or the state of activity of nuclear genes can be responsible for the morphological differences, but demonstrate instead that the "hereditary information" underlying the differences in cortical patterns is stored and transmitted by structures associated with the cortex itself.The crucial questions are those concerning the mechanism of maintenance of cortical specificity.Persistent reports of DNA associated with the ciliate cortex (see e.g.RANDALL and DISBREY 1965) lend plausibility to the suggestion (see LWOFF 1950) that gene-like elements imbedded in the cortex represent peripheral ' This study was supported by grants from the Public Health Service (GM-07779).