OMIA:001101-9031 : Ribosomal RNA deficiency in Gallus gallus (chicken)

Categories: Mortality / aging (incl. embryonic lethal)

Links to possible relevant human trait(s) and/or gene(s) in OMIM: 180450 (gene) , 180451 (gene) , 180452 (gene) , 180453 (gene) , 180454 (gene)

Mendelian trait/disorder: yes

Mode of inheritance: Autosomal recessive lethal

Considered a defect: yes

Key variant known: yes

Year key variant first reported: 1994

Species-specific description: The chicken genome contains just one nucleolar organiser region (NOR), i.e. just one cluster of genes encoding ribosomal RNA. It is located on chromsome 16. The normal chicken NOR consist of approximately 145 copies of ribosomal RNA genes, each approximately 40 kb (Delany, Muscarella and Bloom, 1994). In 1991, Delaney et al. reported a mutant NOR allele with significantly fewer RNA genes. This mutant is maintained in the Polymorphic Nucleolar (PNU) strain at Cornell University. Further studies by Delany, Muscarella and Bloom (1994) showed that the mutant allele (designated p*1) contains only approximately 129 rRNA genes. Homozygotes for this allele have insufficient ribosomal RNA for embryonic development, and consequently die within 24 hours of fertilisation. In contrast, heterozygotes (with approximately 192 copies of rRNA genes) survive as well as homozygous normals. Thus 66% of the normal number of rRNA genes is sufficient for normal embryonic development, but 45% is not sufficient. Since the NOR is on an autosome, and since heterozygotes are normal, this disorder is an autosomal recessive embryonic lethal.

Associated gene:

Symbol Description Species Chr Location OMIA gene details page Other Links
NOR nucleolus organizer region Gallus gallus - no genomic information (-..-) NOR Homologene, Ensembl , NCBI gene


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WARNING! Inclusion of a variant in this table does not automatically mean that it should be used for DNA testing. Anyone contemplating the use of any of these variants for DNA testing should examine critically the relevant evidence (especially in breeds other than the breed in which the variant was first described). If it is decided to proceed, the location and orientation of the variant sequence should be checked very carefully.

Since October 2021, OMIA includes a semiautomated lift-over pipeline to facilitate updates of genomic positions to a recent reference genome position. These changes to genomic positions are not always reflected in the ‘acknowledgements’ or ‘verbal description’ fields in this table.

OMIA Variant ID Breed(s) Variant Phenotype Gene Allele Type of Variant Source of Genetic Variant Reference Sequence Chr. g. or m. c. or n. p. Verbal Description EVA ID Year Published PubMed ID(s) Acknowledgements
664 Polymorphic Nucleolar [PNU] strain, United States of America (Chicken) Ribosomal RNA deficiency NOR deletion, gross (>20) Naturally occurring variant "Embryos exhibiting a nucleolar phenotype of one large and one very small nucleolus (Pp) are heterozygous for a reduced rDNA cluster (+/p1) and were shown in the present study to contain about 66% of the complement of rRNA genes in normal individuals (+/+) that show two large equal-sized nucleoli (PP)" 1994 8014461

Cite this entry

Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2021). OMIA:001101-9031: Online Mendelian Inheritance in Animals (OMIA) [dataset].


Note: the references are listed in reverse chronological order (from the most recent year to the earliest year), and alphabetically by first author within a year.

2000 Delany, M.E. :
Patterns of ribosomal gene variation in elite commercial chicken pure line populations. Anim Genet 31:110-6, 2000. Pubmed reference: 10782209.
1999 Delany, M.E., Krupkin, A.B. :
Molecular characterization of ribosomal gene variation within and among NORs segregating in specialized populations of chicken. Genome 42:60-71, 1999. Pubmed reference: 10208002.
1998 Su, M.H., Delany, M.E. :
Ribosomal RNA gene copy number and nucleolar-size polymorphisms within and among chicken lines selected for enhanced growth. Poult Sci 77:1748-54, 1998. Pubmed reference: 9872573.
1995 Delany, M.E., Taylor, R.L., Bloom, S.E. :
Teratogenic development in chicken embryos associated with a major deletion in the rRNA gene cluster Development Growth & Differentiation 37:403-412, 1995.
1994 Delany, M.E., Emsley, A., Smiley, M.B., Putnam, J.R., Bloom, S.E. :
Nucleolar Size Polymorphisms in Commercial Layer Chickens - Determination of Incidence, Inheritance, and Nucleolar Sizes Poultry Science 73:1211-1217, 1994. Pubmed reference: 7971662.
Delany, M.E., Muscarella, D.E., Bloom, S.E. :
Effects of rRNA gene copy number and nucleolar variation on early development: Inhibition of gastrulation in rDNA- Deficient chick embryos Journal of Heredity 85:211-217, 1994. Pubmed reference: 8014461.
1991 Delany, M.E., Muscarella, D.E., Bloom, S.E. :
Formation of Nucleolar Polymorphisms in Trisomic Chickens and Subsequent Microevolution of rRNA Gene Clusters in Diploids Journal of Heredity 82:213-220, 1991. Pubmed reference: 2061593.
1987 Muscarella, D.E., Vogt, V.M., Bloom, S.E. :
Characterization of ribosomal RNA synthesis in a gene dosage mutant: the relationship of topoisomerase I and chromatin structure to transcriptional activity Journal of Cell Biology 105:1501-1513, 1987. Pubmed reference: 2822724.

Edit History

  • Created by Frank Nicholas on 12 Sep 2005
  • Changed by Frank Nicholas on 11 Oct 2011
  • Changed by Frank Nicholas on 09 Dec 2011
  • Changed by Frank Nicholas on 29 Jan 2018
  • Changed by Imke Tammen2 on 27 May 2021