期刊
CHROMOSOME RESEARCH
卷 8, 期 4, 页码 305-311出版社
KLUWER ACADEMIC PUBL
DOI: 10.1023/A:1009227427575
关键词
B-chromosomes; black rat; NORs; rDNA; supernumerary chromosomes
In-situ hybridization with a rDNA probe has demonstrated the presence of non-transcribed ribosomal genes in the B chromosomes of the black rat Rattus rattus. To test whether methylation of ribosomal DNA present in the B chromosomes could account for their inactivation, we performed in-situ digestions and Southern analyses of DNA digested with the isoschizomers MspI and HpaII. Our results suggest that the accessory chromosomes of this species have originated from one of the smaller NOR-carrying chromosome pairs. In the course of evolution, repetitive sequences invaded this supernumerary element and its ribosomal DNA content was dispersed throughout the chromosome and inactivated by heterochromatinization and methylation.
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