Nucleolar dominance and replicative dominance in Drosophila interspecific hybrids.

Abstract The replication of the rDNA complement of only one nucleolus organizer region during polytene chromosome formation (replicative dominance) was initially observed in Drosophila melanogaster. Here we demonstrate replicative dominance in Drosophila simulans and D. melanogaster/D. simulans interspecific hybrids. A second nucleolar phenomenon, nucleolar dominance, is observed in the diploid tissue of interspecific hybrids. In this case only one of two nucleolus organizer regions forms a nucleolus. However, reorganizations of the X chromosome heterochromatin which eliminate nucleolar dominance have no apparent effect on the expression of replicative dominance. These observations lead us to conclude that nucleolar dominance and replicative dominance are operationally separable functions influencing the rDNAs, and may be determined by differing regulatory events.

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Genetic studies on nucleolus organizer regions (NORs) in cattle

Genetics Research ◽

10.1017/s0016672300027993 ◽

1989 ◽

Vol 53 (2) ◽

pp. 111-118 ◽

Cited By ~ 1

Author(s):

B. Mayr ◽

K. Gruber ◽

G. Brem ◽

G. Mayrhofer

Keyword(s):

Organizer Region ◽

Nucleolus Organizer Region ◽

Monozygotic Twins ◽

Peripheral Blood Lymphocytes ◽

Nucleolus Organizer ◽

Genetic Studies ◽

Nucleolus Organizer Regions ◽

Opposite Sex ◽

High Heritability ◽

The Individual

SummaryExperimentally produced monozygotic twins, natural opposite sex blood chimeras (freemartins), and several pedigrees were used to evaluate the genetic influences on the nucleolus organizer region (NOR) patterns in cattle. In monozygotic twins, the NOR patterns of both twins are extremely similar. In chimeras, NOR patterns of genetically identical, peripheral blood lymphocytes (PBL) from the two partners resemble each other. In contrast, genetically different PBL (sib organ) differ significantly in the same environment. A high heritability of the individual NOR patterns is also demonstrated in our 23 pedigrees. In conclusion, our data demonstrate that variation in NOR expression is predominantly due to genetic factors.

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Genetic control of 1R nucleolus organizer region expression in the presence of wheat genomes

Genome ◽

10.1139/g90-107 ◽

1990 ◽

Vol 33 (5) ◽

pp. 713-718 ◽

Cited By ~ 32

Author(s):

Rita Vieira ◽

Álvaro Queiroz ◽

Leonor Morais ◽

Augusta Barão ◽

T. Mello-Sampayo ◽

...

Keyword(s):

Genetic Control ◽

Hexaploid Wheat ◽

Organizer Region ◽

Nucleolus Organizer Region ◽

Nucleolus Organizer ◽

Rrna Genes ◽

Root Tip ◽

Region Gene ◽

Nucleolar Dominance ◽

Chromosome 1R

The expression of rRNA genes located in the nucleolar organizing region (NOR) present on the short arm of chromosome 1R from rye (Secale cereale L.) was examined in several hexaploid (Triticum aestivum L.) and tetraploid wheats (Triticum turgidum L.) containing the entire chromosome 1R from rye (disomic substitution 1B(1R)), its full haploid genome (hexaploid wheat–rye F1 hybrid), or only its short arm translocated to the long arms of wheat chromosomes from the homoeologous group 1 (disomic translocations 1AL/1RS, 1BL/1RS, or 1DL/1RS) or added to the complete hexaploid wheat genotype (monotelosomic addition 1RS). By silver staining and determination of the number of Ag-NORs and the average number of nucleoli per root-tip cell it became apparent that the expression of 1R NORs, in the presence of wheat genomes, depends on the absence of the long arm of rye chromosome 1R. In wheat-rye F1 hybrids and in hexaploid wheat with a disomic substitution 1B(1R), 1R NOR was morphologically absent, even when only one wheat major NOR was present, in contrast with its frequent expression in wheat–rye translocation or addition lines where only its short arm was added. It is suggested that wheat nucleolar dominance over rye as expressed by heterochromatic and silent NOR in 1RS is under a complex genetic control which involves interaction between 1RL and unidentified wheat genes.Key words: 1R nucleolus organizer region, gene activity, amphiplasty.

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First cytogenetic characterization of the Amazon Catfish Leiarius marmoratus (Gill, 1870) and its hybrid with Pseudoplatystoma reticulatum (Eigenmann & Eigenmann, 1889)

Caryologia ◽

10.36253/caryologia-1149 ◽

2021 ◽

Vol 74 (1) ◽

pp. 127-133

Author(s):

Fernanda Dotti do Prado ◽

Andrea Abrigato de Freitas Mourão ◽

Fausto Foresti ◽

José Augusto Senhorini ◽

Fabio Porto-Foresti

Keyword(s):

Organizer Region ◽

Nucleolus Organizer Region ◽

5S Rdna ◽

Nucleolus Organizer ◽

Intraindividual Variation ◽

Nucleolar Dominance ◽

Rdna Sites ◽

Telocentric Chromosomes ◽

Cytogenetic Characterization

This study reports the first cytogenetic characterization of the Amazonian catfish Leiarius marmoratus (“jandiá”) and its F1 (first generation) hybrid “cachandiá” with Pseudoplatystoma reticulatum (“cachara”). A diploid number of 56 chromosomes and a single argyrophilic nucleolus organizer region (Ag-NOR) in the short arm of two sub-telocentric chromosomes were observed for both L. marmoratus and P. reticulatum, but with differences in the karyotype formula and the size of the chromosome pair with NORs. The hybrid showed 2n = 56 chromosomes with an intermediate karyotype when compared to the parental species. A single Ag-NOR was maintained in the hybrid but located in two chromosomes with marked differences in size and presenting intraindividual variation in NOR activity (nucleolar dominance). For L. marmoratus and the hybrid, heterochromatic bands were predominately distributed in the terminal, centromeric, and sub-centromeric regions of some chromosomes and 5S rDNA sites located in two distinct sub-telocentric chromosomes, similar to the previously described for P. reticulatum. The data suggested that the hybrid karyotype might be insufficient for a precise discrimination of hybrids, however, Ag-NOR can be used as a chromosome marker to differentiate “cachandiá” from L. marmoratus and P. reticulatum. The current study also provides insights into the chromosomal features of L. marmoratus and contributes with novel cytogenetic information of this native Amazonian catfish included in the Pimelodidae family.

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Relative abundance of various rDNA repeat types in polytene nuclei of Drosophila melanogaster

Genome ◽

10.1139/g90-038 ◽

1990 ◽

Vol 33 (2) ◽

pp. 240-246 ◽

Cited By ~ 2

Author(s):

Karen E. Kalumuck ◽

F. Liebchen Wetzel ◽

James D. Procunier

Keyword(s):

Drosophila Melanogaster ◽

Relative Abundance ◽

Organizer Region ◽

Nucleolus Organizer Region ◽

Distal Portion ◽

Nucleolus Organizer ◽

Major Type ◽

Type I ◽

Dnase I Sensitivity ◽

Polytene Nuclei

The relative abundance of the five predominant X chromosome nucleolus organizer repeat types was determined in polytene nuclei. Previous studies showed that the major type I insert containing class of repeats was disproportionately underreplicated when compared with the insert-free class of repeats in these nuclei. Our results demonstrate that this disproportionate underreplication also occurs for both the minor type I and type II insert containing repeats. There was not an exclusive polytenization of the insert-free repeats for this wild-type X nucleolus organizer region. A repeat type lacking either insert type and having an unusually long nonstrancribed spacer was identified and found to be preferentially replicated in polytene nuclei. Preliminary mapping studies indicate that this class of repeats has a unique location, in the distal portion of either the X nucleolus organizer region or the centric heterochromatin. Their similarity to the common insert-free repeats includes preferential polytenization and generalized DNase I sensitivity, which suggests that they are transcriptionally active.Key words: Drosophila melanogaster, rDNA polytenization.

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LOCALIZATION OF DNA COMPLEMENTARY TO RIBOSOMAL RNA IN THE NUCLEOLUS ORGANIZER REGION OF DROSOPHILA MELANOGASTER

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.53.4.737 ◽

1965 ◽

Vol 53 (4) ◽

pp. 737-745 ◽

Cited By ~ 332

Author(s):

F. M. Ritossa ◽

S. Spiegelman

Keyword(s):

Drosophila Melanogaster ◽

Ribosomal Rna ◽

Organizer Region ◽

Nucleolus Organizer Region ◽

Nucleolus Organizer

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Cytogenetic and identification of the nucleolus organizer region in Heliconia bihai (L.) L.

Revista CERES ◽

10.1590/0034-737x201461040002 ◽

2014 ◽

Vol 61 (4) ◽

pp. 451-457 ◽

Cited By ~ 2

Author(s):

Heloisa Rocha do Nascimento ◽

Ricardo Gallo ◽

Isane Vera Karsburg ◽

Ademilso Sampaio Oliveira

Keyword(s):

Root Meristem ◽

Organizer Region ◽

Acetic Acid Solution ◽

Nucleolus Organizer Region ◽

Diploid Species ◽

Enzymatic Digestion ◽

Nucleolus Organizer ◽

Hot Plate ◽

Nucleolus Organizer Regions ◽

Interphase Cells

The genus Heliconia is not much studied and the number of existing species in this genus is still uncertain. It is known that this number relies between 150 to 250 species. In Brazil, about 40 species are native and known by many different names. The objective of this paper was to characterize morphometrically and to identify the NOR (active nucleolus organizer regions) by Ag-NOR banding of chromosomes of Heliconia bihai (L) L. Root meristems were submitted to blocking treatment in an amiprofos-methyl (APM) solution, fixed in methanol-acetic acid solution for 24 hours, at least. The meristems were washed in distilled water and submitted to enzymatic digestion with pectinase enzyme. The slides were prepared by dissociation of the root meristem, dried in the air and also on hot plate at 50°C. Subsequently, some slides were submitted to 5% Giemsa stain for karyotype construction and to a solution of silver nitrate (AgNO3) 50% for Ag-NOR banding. The species H. bihai has 2n = 22 chromosomes, 4 pairs of submetacentric chromosomes and 7 pairs of metacentric chromosomes, and graded medium to short (3.96 to 0.67 μM), with the presence of active NOR in pairs 1 and 2 and interphase cells with 2 nucleoli. These are the features of a diploid species.

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1R chromosome nucleolus organizer region activation by 5-azacytidine in wheat × rye hybrids

Genome ◽

10.1139/g90-106 ◽

1990 ◽

Vol 33 (5) ◽

pp. 707-712 ◽

Cited By ~ 33

Author(s):

Rita Vieira ◽

Álvaro Queiroz ◽

Leonor Morais ◽

Augusta Barão ◽

T. Mello-Sampayo ◽

...

Keyword(s):

Triticum Turgidum ◽

Organizer Region ◽

Nucleolus Organizer Region ◽

Nucleolar Organizer ◽

Pyrimidine Ring ◽

Nucleolus Organizer ◽

Rrna Genes ◽

Root Tip ◽

Root Tips ◽

Nucleolar Dominance

Nucleolar activity was studied in several lines of Triticum aestivum cv. Chinese Spring, Triticum turgidum cv. Durum, and F1 hybrids from euploid and aneuploid lines of T. aestivum and Secale cereale cv. Centeio do Alto, in cells from root tips of seeds germinated in water or in 5-azacytidine. 5-Azacytidine, an analog of cytidine modified in the 5 position of the pyrimidine ring, inhibits DNA methylation. By using silver staining to determine the number of nucleolus organizer regions and the average number of nucleoli per root-tip cell from seeds germinated in both situations, it became apparent that the presence of 5-azacytidine during germination allowed for the expression of the nucleolus organizer region locus belonging to the rye genome, in contrast to the usual observed cytological absence of the rye nucleolus organizer region in wheat–rye hybrids. It is suggested that wheat nucleolar dominance in wheat–rye hybrids is mainly a consequence of methylation of rRNA genes or its regulators located on the 1R chromosome of rye.Key words: 1R nucleolar organizer, wheat–rye hybrids, methylation, Ag-NOR.

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