We report on a major update to the animal rDNA loci database, which now contains cytogenetic information for 45S and 5S rDNA loci in more than 2600 and 1000 species, respectively.The data analyses show the following: (i) A high variability in 5S and 45S loci numbers, with both showing 50-fold or higher variability. However, karyotypes with an extremely high number of loci were rare, and medians generally converged to two 5S sites and two 45S rDNA sites per diploid genome. No relationship was observed between the number of 5S and 45S loci. (ii) The position of 45S rDNA on sex chromosomes was relatively frequent in some groups, particularly in arthropods (14% of karyotypes). Furthermore, 45S rDNA was almost exclusively located in microchromosomes when these were present (in birds and reptiles). (iii) The proportion of active NORs (positively stained with silver staining methods) progressively decreased with an increasing number of 45S rDNA loci, and karyotypes with more than 12 loci showed, on average, less than 40% of active loci. In conclusion, the updated version of the database provides some new insights into the organization of rRNA genes in chromosomes. We expect that its updated content will be useful for taxonomists, comparative cytogeneticists, and evolutionary biologists. .

Bioscripts Centro de Investigación y Desarrollo de Recursos Científicos 41012 Sevilla Spain

Institut Botànic de Barcelona Passeig del Migdia s n 08038 Barcelona Spain

Institute of Biophysics Academy of Sciences of the Czech Republic 61265 Brno Czech Republic

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Symonova R. Integrative rDNAomics-Importance of the Oldest Repetitive Fraction of the Eukaryote Genome. Genes. 2019;10:345. doi: 10.3390/genes10050345. PubMed DOI PMC

Bersaglieri C., Santoro R. Genome Organization in and around the Nucleolus. Cells. 2019;8:579. doi: 10.3390/cells8060579. PubMed DOI PMC

Kobayashi T. A new role of the rDNA and nucleolus in the nucleus-rDNA instability maintains genome integrity. Bioessays. 2008;30:267–272. doi: 10.1002/bies.20723. PubMed DOI

McClintock B. The relationship of a particular chromosomal element to the development of the nucleoli in Zea mays. Zeitschrift für Zellforschung und mikroskopische Anatomie. 1934;21:294–398. doi: 10.1007/BF00374060. DOI

Gall J.G. Chromosome structure and the C-value paradox. J. Cell Biol. 1981;91:3s–14s. doi: 10.1083/jcb.91.3.3s. PubMed DOI PMC

Baumlein H., Wobus U. Chromosomal Localization of Ribosomal 5S Rna Genes in Chironomus-Thumni by in Situ Hybridization of Iodinated 5s Rna. Chromosoma. 1976;57:199–204. doi: 10.1007/BF00292918. PubMed DOI

Schweizer D., Mendelak M., White M.J.D., Contreras N. Cytogenetics of the parthenogenetic grasshopper Warramaba virgo and its bisexual relatives. Chromosoma. 1983;88:227–236. doi: 10.1007/BF00285625. DOI

Bauman J.G.J., Wiegant J., Borst P., Vanduijn P. A New Method for Fluorescence Microscopical Localization of Specific DNA-Sequences by Insitu Hybridization of Fluorochrome-Labeled Rna. Exp. Cell Res. 1980;128:485–490. doi: 10.1016/0014-4827(80)90087-7. PubMed DOI

Cabral-de-Mello D.C., Marec F. Universal fluorescence in situ hybridization (FISH) protocol for mapping repetitive DNAs in insects and other arthropods. Mol. Genet. Genom. 2021;296:513–526. doi: 10.1007/s00438-021-01765-2. PubMed DOI

Alves-Silva A.P., Barros L.A.C., das Graças Pompolo S. General Protocol of FISH for Insects. In: Liehr T., editor. Fluorescence In Situ Hybridization (FISH): Application Guide. Springer; Berlin/Heidelberg, Germany: 2017. pp. 459–466.

Yano C.F., Bertollo L.A.C., de Bello Cioffi M. Fish-FISH: Molecular Cytogenetics in Fish Species. In: Liehr T., editor. Fluorescence In Situ Hybridization (FISH): Application Guide. Springer; Berlin/Heidelberg, Germany: 2017. pp. 429–443.

Garcia S., Kovarik A., Leitch A.R., Garnatje T. Cytogenetic features of rRNA genes across land plants: Analysis of the Plant rDNA database. Plant J. 2017;89:1020–1030. doi: 10.1111/tpj.13442. PubMed DOI

Sochorova J., Garcia S., Galvez F., Symonova R., Kovarik A. Evolutionary trends in animal ribosomal DNA loci: Introduction to a new online database. Chromosoma. 2018;127:141–150. doi: 10.1007/s00412-017-0651-8. PubMed DOI PMC

Roa F., Guerra M. Non-Random Distribution of 5S rDNA Sites and Its Association with 45S rDNA in Plant Chromosomes. Cytogenet. Genome Res. 2015;146:243–249. doi: 10.1159/000440930. PubMed DOI

Drosopoulou E., Nakou I., Sichova J., Kubickova S., Marec F., Mavragani-Tsipidou P. Sex chromosomes and associated rDNA form a heterochromatic network in the polytene nuclei of Bactrocera oleae (Diptera: Tephritidae) Genetica. 2012;140:169–180. doi: 10.1007/s10709-012-9668-3. PubMed DOI

Bombarova M., Marec F., Nguyen P., Spakulova M. Divergent location of ribosomal genes in chromosomes of fish thorny-headed worms, Pomphorhynchus laevis and Pomphorhynchus tereticollis (Acanthocephala) Genetica. 2007;131:141–149. doi: 10.1007/s10709-006-9124-3. PubMed DOI

Marques A., Klemme S., Houben A. Evolution of Plant B Chromosome Enriched Sequences. Genes. 2018;9:515. doi: 10.3390/genes9100515. PubMed DOI PMC

Utsunomia R., Silva D.M., Ruiz-Ruano F.J., Araya-Jaime C., Pansonato-Alves J.C., Scacchetti P.C., Hashimoto D.T., Oliveira C., Trifonov V.A., Porto-Foresti F., et al. Uncovering the Ancestry of B Chromosomes in Moenkhausia sanctaefilomenae (Teleostei, Characidae) PLoS ONE. 2016;11:e0150573. doi: 10.1371/journal.pone.0150573. PubMed DOI PMC

Keller I., Chintauan-Marquier I.C., Veltsos P., Nichols R.A. Ribosomal DNA in the grasshopper Podisma pedestris: Escape from concerted evolution. Genetics. 2006;174:863–874. doi: 10.1534/genetics.106.061341. PubMed DOI PMC

Wang W.C., Ma L., Becher H., Garcia S., Kovarikova A., Leitch I.J., Leitch A.R., Kovarik A. Astonishing 35S rDNA diversity in the gymnosperm species Cycas revoluta Thunb. Chromosoma. 2016;125:683–699. doi: 10.1007/s00412-015-0556-3. PubMed DOI PMC

Garcia S., Garnatje T., Kovarik A. Plant rDNA database: Ribosomal DNA loci information goes online. Chromosoma. 2012;121:389–394. doi: 10.1007/s00412-012-0368-7. PubMed DOI

RStudio Team . RStudio: Integrated Development Environment for R. RStudio, PBC; Boston, MA, USA: 2021. [(accessed on 2 May 2021)]. Available online: http://www.rstudio.com/

Mann Whitney U Test Calculator. 2017. [(accessed on 10 September 2021)]. Statistics Kingdom. Available online: http://www.statskingdom.com/170median_mann_whitney.html.

Levene’s Test. 2017. [(accessed on 10 September 2021)]. Statistics Kingdom. Available online: https://www.statskingdom.com/230var_levenes.html.

IUCN The IUCN Red List of Threatened Species. Version 2021-2. [(accessed on 1 June 2021)]. Available online: https://www.iucnredlist.org.

Degrandi T.M., Gunski R.J., Garnero A.D., de Oliveira E.H.C., Kretschmer R., de Souza M.S., Barcellos S.A., Hass I. The distribution of 45S rDNA sites in bird chromosomes suggests multiple evolutionary histories. Genet. Mol. Biol. 2020;43 doi: 10.1590/1678-4685-gmb-2018-0331. PubMed DOI PMC

Zhang Z.Q. Phylum Arthropoda. Zootaxa. 2013;3703:17–26. doi: 10.11646/zootaxa.3703.1.6. DOI

Stahlavsky F., Nguyen P., Sadilek D., Stundlova J., Just P., Haddad C.R., Koc H., Ranawana K.B., Stockmann M., Yagmur E.A., et al. Evolutionary dynamics of rDNA clusters on chromosomes of buthid scorpions (Chelicerata: Arachnida) Biol. J. Linn. Soc. 2020;131:547–565. doi: 10.1093/biolinnean/blaa118. DOI

Sichova J., Nguyen P., Dalikova M., Marec F. Chromosomal evolution in Tortricid moths: Conserved karyotypes with diverged features. PLoS ONE. 2013;8:e64520. doi: 10.1371/journal.pone.0064520. PubMed DOI PMC

Roy V., Monti-Dedieu L., Chaminade N., Siljak-Yakovlev S., Aulard S., Lemeunier F., Montchamp-Moreau C. Evolution of the chromosomal location of rDNA genes in two Drosophila species subgroups: Ananassae and melanogaster. Heredity. 2005;94:388–395. doi: 10.1038/sj.hdy.6800612. PubMed DOI

Cabral-de-Mello D.C., Cabrero J., Lopez-Leon M.D., Camacho J.P.M. Evolutionary dynamics of 5S rDNA location in acridid grasshoppers and its relationship with H3 histone gene and 45S rDNA location. Genetica. 2011;139:921–931. doi: 10.1007/s10709-011-9596-7. PubMed DOI

Cazaux B., Catalan J., Veyrunes F., Douzery E.J.P., Britton-Davidian J. Are ribosomal DNA clusters rearrangement hotspots? A case study in the genus Mus (Rodentia, Muridae) BMC Evol. Biol. 2011;11:124. doi: 10.1186/1471-2148-11-124. PubMed DOI PMC

Rebordinos L., Cross I., Merlo A. High evolutionary dynamism in 5S rDNA of fish: State of the art. Cytogenet. Genome Res. 2013;141:103–113. doi: 10.1159/000354871. PubMed DOI

Roa F., Guerra M. Distribution of 45S rDNA sites in chromosomes of plants: Structural and evolutionary implications. BMC Evol. Biol. 2012;12:225. doi: 10.1186/1471-2148-12-225. PubMed DOI PMC

Ishijima J., Uno Y., Nunome M., Nishida C., Kuraku S., Matsuda Y. Molecular cytogenetic characterization of chromosome site-specific repetitive sequences in the Arctic lamprey (Lethenteron camtschaticum, Petromyzontidae) DNA Res. 2017;24:93–101. doi: 10.1093/dnares/dsw053. PubMed DOI PMC

Covelo-Soto L., Moran P., Pasantes J.J., Perez-Garcia C. Cytogenetic evidences of genome rearrangement and differential epigenetic chromatin modification in the sea lamprey (Petromyzon marinus) Genetica. 2014;142:545–554. doi: 10.1007/s10709-014-9802-5. PubMed DOI

Caputo V., Giovannotti M., Cerioni P.N., Splendiani A., Tagliavini J., Olmo E. Chromosomal study of a lamprey (Lampetra zanandreai Vladykov, 1955) (Petromyzonida: Petromyzontiformes): Conventional and FISH analysis. Chromosome Res. 2011;19:481–491. doi: 10.1007/s10577-011-9197-4. PubMed DOI

Mlinarec J., Muzic M., Pavlica M., Srut M., Klobucar G., Maguire I. Comparative karyotype investigations in the European crayfish Astacus astacus and A. leptodactylus (Decapoda, Astacidae) Crustaceana. 2011;84:1497–1510.

Fontana F., Lanfredi M., Congiu L., Leis M., Chicca M., Rossi R. Chromosomal mapping of 18S-28S and 5S rRNA genes by two-colour fluorescent in situ hybridization in six sturgeon species. Genome. 2003;46:473–477. doi: 10.1139/g03-007. PubMed DOI

Hall A.N., Turner T.N., Queitsch C. Thousands of high-quality sequencing samples fail to show meaningful correlation between 5S and 45S ribosomal DNA arrays in humans. Sci. Rep. 2021;11:449. doi: 10.1038/s41598-020-80049-y. PubMed DOI PMC

Gibbons J.G., Branco A.T., Godinho S.A., Yu S., Lemos B. Concerted copy number variation balances ribosomal DNA dosage in human and mouse genomes. Proc. Natl. Acad. Sci. USA. 2015;112:2485–2490. doi: 10.1073/pnas.1416878112. PubMed DOI PMC

Panzera F., Pita S., Nattero J., Panzera Y., Galvao C., Chavez T., De Arias A.R., Tellez L.C., Noireau F. Cryptic speciation in the Triatoma sordida subcomplex (Hemiptera, Reduviidae) revealed by chromosomal markers. Parasite Vector. 2015;8:495. doi: 10.1186/s13071-015-1109-6. PubMed DOI PMC

Hennig W., Link B., Leoncini O. Location of Nucleolus Organizer Regions in Drosophila-Hydei. Chromosoma. 1975;51:57–63. doi: 10.1007/BF00285808. PubMed DOI

Marchi A.G., Messi G., Renier S., Gallone G., Peisino M.G., Viettiramus M., Raspino M., Chiossi M., Lattere M., Polla D. The risk associated with poisonings in children. Vet. Hum. Toxicol. 1994;36:112–116. PubMed

Brianti M.T., Ananina G., Recco-Pimentel S.M., Klaczko L.B. Comparative analysis of the chromosomal positions of rDNA genes in species of the tripunctata radiation of Drosophila. Cytogenet. Genome Res. 2009;125:149–157. PubMed

Kuznetsova V.G., Khabiev G.N., Anokhin B.A. Cytogenetic study on antlions (Neuroptera, Myrmeleontidae): First data on telomere structure and rDNA location. Comp. Cytogenet. 2016;10:647–656. doi: 10.3897/CompCytogen.v10i4.10775. PubMed DOI PMC

Lohe A.R., Roberts P.A. Evolution of DNA in heterochromatin: The Drosophila melanogaster sibling species subgroup as a resource. Genetica. 2000;109:125–130. doi: 10.1023/A:1026588217432. PubMed DOI

Stitou S., Burgos M., Zurita F., Jimenez R., Sanchez A., Diaz de la Guardia R. Recent evolution of NOR-bearing and sex chromosomes of the North African rodent Lemniscomys barbarus. Chromosome Res. 1997;5:481–485. doi: 10.1023/A:1018473131446. PubMed DOI

Maffei E.M.D., Pompolo S.D.G., Campos L.A.D., Petitpierre E. Sequential FISH analysis with rDNA genes and Ag-NOR banding in the lady beetle Olla v-nigrum (Coleoptera: Coccinellidae) Hereditas. 2001;135:13–18. doi: 10.1111/j.1601-5223.2001.00013.x. PubMed DOI

Raudsepp T. Cytogenetics and Infertility. In: Cebra C., Anderson D.E., Tibary A., Van Saun R.J., Johnson L.W., editors. Llama and Alpaca Care. W.B. Saunders; St. Louis, MO, USA: 2014. pp. 243–249. Chapter 21.

Paredes S., Branco A.T., Hartl D.L., Maggert K.A., Lemos B. Ribosomal DNA deletions modulate genome-wide gene expression: “rDNA-sensitive” genes and natural variation. PLoS Genet. 2011;7:e1001376. doi: 10.1371/journal.pgen.1001376. PubMed DOI PMC

Nguyen P., Sahara K., Yoshido A., Marec F. Evolutionary dynamics of rDNA clusters on chromosomes of moths and butterflies (Lepidoptera) Genetica. 2010;138:343–354. doi: 10.1007/s10709-009-9424-5. PubMed DOI

Bizzaro D., Mandrioli M., Zanotti M., Giusti M., Manicardi G.C. Chromosome analysis and molecular characterization of highly repeated DNAs in the aphid Acyrthosiphon pisum (Aphididae, Hemiptera) Genetica. 2000;108:197–202. doi: 10.1023/A:1004128314728. PubMed DOI

Blanco D.R., Vicari M.R., Lui R.L., Artoni R.F., de Almeida M.C., Traldi J.B., Margarido V.P., Moreira O. Origin of the X1X1X2X2/X1X2Y sex chromosome system of Harttia punctata (Siluriformes, Loricariidae) inferred from chromosome painting and FISH with ribosomal DNA markers. Genetica. 2014;142:119–126. doi: 10.1007/s10709-014-9759-4. PubMed DOI

Bardella V.B., Fernandes J.A.M., Cabral-de-Mello D.C. Chromosomal evolutionary dynamics of four multigene families in Coreidae and Pentatomidae (Heteroptera) true bugs. Mol. Genet. Genom. 2016;291:1919–1925. doi: 10.1007/s00438-016-1229-5. PubMed DOI

Symonova R., Majtanova Z., Sember A., Staaks G.B.O., Bohlen J., Freyhof J., Rabova M., Rab P. Genome differentiation in a species pair of coregonine fishes: An extremely rapid speciation driven by stress-activated retrotransposons mediating extensive ribosomal DNA multiplications. BMC Evol. Biol. 2013;13:42. doi: 10.1186/1471-2148-13-42. PubMed DOI PMC

Raskina O., Belyayev A., Nevo E. Activity of the En/Spm-like transposons in meiosis as a base for chromosome repatterning in a small, isolated, peripheral population of Aegilops speltoides Tausch. Chromosome Res. 2004;12:153–161. doi: 10.1023/B:CHRO.0000013168.61359.43. PubMed DOI

Ruiz-Estevez M., Lopez-Leon M.D., Cabrero J., Camacho J.P.M. B-Chromosome ribosomal DNA is functional in the grasshopper Eyprepocnemis plorans. PLoS ONE. 2012;7:e36600. doi: 10.1371/journal.pone.0036600. PubMed DOI PMC

Ezaz T., Young M. Microchromosomes. In: Maloy S., Hughes K., editors. Brenner’s Encyclopedia of Genetics. 2nd ed. Academic Press; San Diego, CA, USA: 2013. pp. 405–407.

Griffin D.K., Robertson L.B.W., Tempest H.G., Skinner B.M. The evolution of the avian genome as revealed by comparative molecular cytogenetics. Cytogenet. Genome Res. 2007;117:64–77. PubMed

Dyomin A.G., Koshel E.I., Kiselev A.M., Saifitdinova A.F., Galkina S.A., Fukagawa T., Kostareva A.A., Gaginskaya E.R. Chicken rRNA Gene Cluster Structure. PLoS ONE. 2016;11:e0157464. doi: 10.1371/journal.pone.0157464. PubMed DOI PMC

Nishida C., Ishijima J., Kosaka A., Tanabe H., Habermann F.A., Griffin D.K., Matsuda Y. Characterization of chromosome structures of Falconinae (Falconidae, Falconiformes, Aves) by chromosome painting and delineation of chromosome rearrangements during their differentiation. Chromosome Res. 2008;16:171–181. doi: 10.1007/s10577-007-1210-6. PubMed DOI

de Oliveira E.H.C., Tagliarini M.M., dos Santos M.S., O’Brien P.C.M., Ferguson-Smith M.A. Chromosome Painting in Three Species of Buteoninae: A Cytogenetic Signature Reinforces the Monophyly of South American Species. PLoS ONE. 2013;8:e70071. doi: 10.1371/journal.pone.0070071. PubMed DOI PMC

Degrandi T.M., Barcellos S.A., Costa A.L., Garnero A.D.V., Hass I., Gunski R.J. Introducing the Bird Chromosome Database: An overview of cytogenetic studies in birds. Cytogenet. Genome Res. 2020;160:199–205. doi: 10.1159/000507768. PubMed DOI

Green R.E., Braun E.L., Armstrong J., Earl D., Nguyen N., Hickey G., Vandewege M.W., St John J.A., Capella-Gutiérrez S., Castoe T.A., et al. Three crocodilian genomes reveal ancestral patterns of evolution among archosaurs. Science. 2014;346:1254449. doi: 10.1126/science.1254449. PubMed DOI PMC

Kawagoshi T., Nishida C., Ota H., Kumazawa Y., Endo H., Matsuda Y. Molecular structures of centromeric heterochromatin and karyotypic evolution in the Siamese crocodile (Crocodylus siamensis) (Crocodylidae, Crocodylia) Chromosome Res. 2008;16:1119–1132. doi: 10.1007/s10577-008-1263-1. PubMed DOI

King M., Honeycutt R., Contreras N. Chromosomal repatterning in crocodiles: C, G and N-banding and the in situ hybridization of 18S and 26S rRNA cistrons. Genetica. 1986;70:191–201. doi: 10.1007/BF00122186. DOI

Porter C.A., Haiduk M.W., Dequeiroz K. Evolution and phylogenetic significance of ribosomal gene location in chromosomes of squamate reptiles. Copeia. 1994;1994:302–313. doi: 10.2307/1446980. DOI

Andreozzi L., Federico C., Motta S., Saccone S., Sazanova A.L., Sazanov A.A., Smirnov A.F., Galkina S.A., Lukina N.A., Rodionov A.V., et al. Compositional mapping of chicken chromosomes and identification of the gene-richest regions. Chromosome Res. 2001;9:521–532. doi: 10.1023/A:1012436900788. PubMed DOI

Smith J., Bruley C.K., Paton I.R., Dunn I., Jones C.T., Windsor D., Morrice D.R., Law A.S., Masabanda J., Sazanov A., et al. Differences in gene density on chicken macrochromosomes and microchromosomes. Anim. Genet. 2000;31:96–103. doi: 10.1046/j.1365-2052.2000.00565.x. PubMed DOI

Burt D.W. Origin and evolution of avian microchromosomes. Cytogenet. Genome Res. 2002;96:97–112. PubMed

Gunski R.J., Kretschmer R., de Souza M.S., Furo I.D., Barcellos S.A., Costa A.L., Cioffi M.B., de Oliveira E.H.C., Garnero A.D. Evolution of Bird Sex Chromosomes Narrated by Repetitive Sequences: Unusual W Chromosome Enlargement in Gallinula melanops (Aves: Gruiformes: Rallidae) Cytogenet. Genome Res. 2019;158:152–159. doi: 10.1159/000501381. PubMed DOI

dos Santos M.D., Kretschmer R., Silva F.A.O., Ledesma M.A., O’Brien P.C.M., Ferguson-Smith M.A., Garnero A.D., de Oliveira E.H.C., Gunski R.J. Intrachromosomal rearrangements in two representatives of the genus Saltator (Thraupidae, Passeriformes) and the occurrence of heteromorphic Z chromosomes. Genetica. 2015;143:535–543. doi: 10.1007/s10709-015-9851-4. PubMed DOI

Cavalcante M.G., Nagamachi C.Y., Pieczarka J.C., Noronha R.C.R. Evolutionary insights in Amazonian turtles (Testudines, Podocnemididae): Co-location of 5S rDNA and U2 snRNA and wide distribution of Tc1/Mariner. Biol. Open. 2020;9:bio049817. doi: 10.1242/bio.049817. PubMed DOI PMC

Vitelli L., Batistoni R., Andronico F., Nardi I., Barsacchi-Pilone G. Chromosomal localization of 18S + 28S and 5S Ribosomal RNA genes in evolutionarily diverse anuran amphibians. Chromosoma. 1982;84:475–491. doi: 10.1007/BF00292849. PubMed DOI

Grummt I., Pikaard C.S. Epigenetic silencing of RNA polymerase I transcription. Nat. Rev. Mol. Cell Biol. 2003;4:641–649. doi: 10.1038/nrm1171. PubMed DOI

Barth A., Souza V.A., Sole M., Costa M.A. Molecular cytogenetics of nucleolar organizer regions in Phyllomedusa and Phasmahyla species (Hylidae, Phyllomedusinae): A cytotaxonomic contribution. Genet. Mol. Res. 2013;12:2400–2408. doi: 10.4238/2013.July.15.3. PubMed DOI

Goodpasture C., Bloom S.E. Visualization of nucleolar organizer regions im mammalian chromosomes using silver staining. Chromosoma. 1975;53:37–50. doi: 10.1007/BF00329389. PubMed DOI

Moreno F.J., Rodrigo R.M., Garcia-Herdugo G. Ag-NOR proteins and rDNA transcriptional activity in plant cells. J. Histochem. Cytochem. 1990;38:1879–1887. doi: 10.1177/38.12.1701461. PubMed DOI

Plate K.H., Ruschoff J., Mennel H.D. Application of the AgNOR technique to neurooncology. Acta Histochem. Suppl. 1992;42:171–178. PubMed

Mohannath G., Pontvianne F., Pikaard C.S. Selective nucleolus organizer inactivation in Arabidopsis is a chromosome position-effect phenomenon. Proc. Natl. Acad. Sci. USA. 2016;113:13426–13431. doi: 10.1073/pnas.1608140113. PubMed DOI PMC

Trerè D. AgNOR staining and quantification. Micron. 2000;31:127–131. doi: 10.1016/S0968-4328(99)00069-4. PubMed DOI

Cabrero J., Camacho J.P.M. Location and expression of ribosomal RNA genes in grasshoppers: Abundance of silent and cryptic loci. Chromosome Res. 2008;16:595–607. doi: 10.1007/s10577-008-1214-x. PubMed DOI

Release 4.0 of the Plant rDNA Database: A Database on Plant Ribosomal DNA Loci Number, Their Position, and Organization: An Information Source for Comparative Cytogenetics