Clonal variation in paramecium. I. Persistent unstable clones.

Clones of Paramecium of identical serotype when cultured in test tubes may differ in their ability to give rise to subclones of this serotype. Characteristically, stable clones yield progeny indistinguishable from their parents, while from unstable clones diverse subclones with new serotypes can be isolated repeatedly. Stable lines are resistant to changes in culture medium and also are unaffected by most sera. In contrast, the numbers and kinds of serotypes displayed among subclones derived from unstable lines are often affected by these same agents. Stable and unstable clones are interconvertible when the medium from individual cultures is repeatedly and frequently replaced by fresh culture fluid. This effect is very likely a result of the removal of the initial exhausted medium with any cell products rather than the addition of fresh nutrient.