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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7547

Stefan Radzikowski; Asynchronous Replication of Polytene Chromosome Segments of the New Macronucleus Anlage in Chilodonella cucullulus O.F. Muller. Protistologica XV(4):521-526, 1979

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Polytene chromosomes occur between 50 and 75 hours after the conjugation process in the developing anlage of the new macronucleus of Chilodonella cucullulus. The asynchronous character of DNA replication of the different parts of polytene chromosomes was demonstrated by using [H3]-thymidine. Seventy five hours from the time the conjugating partners separate the chromosomes undergo transverse and longitudinal fragmentation. During the first division of the exconjugant approximately 35% of the chromatin from the new anlage is eliminated to the cytoplasm. It would appear that chromatin originating from the regions of earlier replicating chromosomes occupies the place in the paramere of the macronucleus, the chromatin of which (euchromatin) replicates earlier in the interdivision cycle. Chromatin occuring in the orthomere (heterochromatin) and replicating later would appear to be a derivative of chromatin from the later replicating regions of polytene chromosomes. The macronucleus is the nucleus which contains only part of the macronuclear genome which, by means of the polytenisation and amplification process, is repeatedly duplicated.