Synopsis. A considerable amount of evidence is now available to indicate that the DNA in the ciliates Oxytricha and Stylonychia undergoes fragmentation when the micronucleus forms a macronucleus. Some evidence suggests that fragmentation may also occur in Tetrahymena and possibly in Paramecium. It is shown that some regulatory or nonrandom segregational mechanism must operate during cell divisions to maintain genic balance in Tetrahymena. Both the hypothesis of macronuclear subunits and also a new hypothesis based on replicative control of DNA are capable of explaining the currently know biochemical, cytological, and genetic facts.
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Preer et al. (1979) studied this question.