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THE ORGANISM Paramecium tetraurelia Eukaryota; Alveolata; Ciliophora; Oligohymenophorea; Peniculida; Paramecium Paramecium is a very large eukaryotic cell (120 micrometers) covered with vibrating cilia. The Ciliates have separate germinal and somatic lineages within a single cytoplasmic unit. These cells possess indeed two nuclei. A germinal nucleus (the micronucleus) is diploid, transcriptionally inactive, contains heterochromatin responsible for the transmission of genetic information via sexual processes. A somatic nucleus (the macronucleus) ensures expression of this information. The macronucleus is derived from the zygotic germline nucleus by programmed DNA rearrangements, is polyploid, has no genetic continuity, consists only of euchromatin, and is the seat of all transcriptional activity. |