Abstract
THE chromosomal nucleolus organiser of Xenopus laevis is a cluster of 450 repeated units, each of which includes sequences complementary to 18S and 28S RNA and a spacer sequence of unknown function1. It is this complex of repeated units, or parts of it, that is amplified through replication over a period of about 20 d during pachytene of early oogenesis, to make a quantity of nucleolar DNA equivalent to eight times the amount of DNA in the whole haploid genome of Xenopus25. The term gene amplification has been applied mainly to the events that begin with the appearance of the extra-chromosomal DNA in the nucleus of a young amphibian oocyte, and lead to the establishment of a multinucleolate condition in which each of the many nucleoli is an independent and physically free object with its own synthetically active DNA component.
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MACGREGOR, H. Amplification, Polytenisation, and Nucleolus Organisers. Nature New Biology 246, 81–82 (1973). https://doi.org/10.1038/newbio246081a0
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DOI: https://doi.org/10.1038/newbio246081a0
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