An Analysis of Nuclear Differentiation in the Selfers of Tetrahymena

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Abstract
Properties of certain unstable clones (selfers) of Family A, variety 1, of T. pyriformis are described in qualitative and quantiative terms. Dual associations of mating types are frequently found in these clones, and cells, pure for one of the mating types, are produced. The rates of production of the 2 types of pure cells from unstable clones, although initially dissimilar, become similar after 100 or more fissions. The sum of the 2 rates, however, comes to an early equilibrium. These properties are interpreted on the assumption that segregation of stable and differentiated macronuclear elements (sub-nuclei) occurs during vegetative reproduction. The accompanying paper by SCHENSTED provides the mathematical basis for evaluating this interpretation precisely, and, in general, the mathematical model and the experimental results are in excellent agreement. The total number of diploid sub-nuclei in a newly divided cell is estimated at 45.