Definitions for nucleolus organizer region
nu·cle·o·lus or·ga·niz·er re·gion

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1. Nucleolus organizer region

   Nucleolus organizer regions (NORs) are chromosomal regions crucial for the formation of the nucleolus. In humans, the NORs are located on the short arms of the acrocentric chromosomes 13, 14, 15, 21 and 22, the genes RNR1, RNR2, RNR3, RNR4, and RNR5 respectively. These regions code for 5.8S, 18S, and 28S ribosomal RNA. The NORs are "sandwiched" between the repetitive, heterochromatic DNA sequences of the centromeres and telomeres. The exact sequence of these regions is not included in the human reference genome as of 2016 or the GRCh38.p10 released January 6, 2017. On 28 February 2019, GRCh38.p13 was released, which added the NOR sequences for the short arms of chromosomes 13, 14, 15, 21, and 22. However, it is known that NORs contain tandem copies of ribosomal DNA (rDNA) genes. Some sequences of flanking sequences proximal and distal to NORs have been reported. The NORs of a loris have been reported to be highly variable. There are also DNA sequences related to rDNA that are on other chromosomes and may be involved in nucleoli formation.

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1. Nucleolus organizer region

   The nucleolus organizer region or nucleolar organizer is a chromosomal region around which the nucleolus forms. This region is the particular part of a chromosome that is associated with a nucleolus after the nucleus divides. The region contains several tandem copies of ribosomal DNA genes. In humans, the NOR contains genes for 5.8S, 18S, and 28S rRNA clustered on the short arms of chromosomes 13, 14, 15, 21 and 22. Nucleolus organizer regions are head-to-tail arrays of genes encoding the precursor of the three largest ribosomal RNAs. NORs include active rRNA genes, which give rise to secondary constrictions of metaphase chromosomes, and silent rRNA genes, which are often highly compacted in dense heterochromatin. At metaphase, a proteinaceous remnant of the nucleolus often remains associated with the secondary constriction. Each rRNA gene at a NOR is nearly identical in sequence, although variation in size due to differences in the number of repeated DNA elements in the intergenic spacer region is common. In complete chromosome complements there were always 6 chromosomes with a terminal Nucleolus organizing region. In most cases part of the NOR was decondensed, and several of this decondensed areas formed together a big collecting nucleolus. This collecting nucleolus was easily visible in phase contrast even without pretreatment due to its large size and particular structure. The shape of the collecting nucleolus ranged from nearly circular to irregular. Instead of just one collecting nucleolus of 6 NOR there were also several smaller collecting nucleoli made up from the NORs of only 2 to 5 nucleolus organizing chromosomes.

U.S. National Library of MedicineRate this definition:0.0 / 0 votes

1. Nucleolus Organizer Region

   The chromosome region which is active in nucleolus formation and which functions in the synthesis of ribosomal RNA.

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Numerology

1. Chaldean Numerology

   The numerical value of nucleolus organizer region in Chaldean Numerology is: 7

2. Pythagorean Numerology

   The numerical value of nucleolus organizer region in Pythagorean Numerology is: 6

References

1. ^ Wikipedia
   https://en.wikipedia.org/wiki/Nucleolus_Organizer_Region
2. ^ Wikidata
   https://www.wikidata.org/w/index.php?search=nucleolus organizer region