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A ring chromosome is an aberrant
In order for a chromosome to form a ring, both ends of the chromosome are usually missing, enabling the broken ends to fuse together. In rare cases, the Shchelochkov O et al.
Mosaicism for r(X) and der(X)del(X)(p11.23)dup(X)(p11.21p11.22) Provides Insight into the Possible Mechanism of Rearrangement, ''Molecular Cytogenetics'' 2008, 1:16 Small supernumary rings can also form, resulting in a partial trisomy. Ring chromosomes are unstable during cell division and can form interlocking or fused rings.
Atlas of Genetics and Cytogenetics in Oncology and Haematology
explains HOW the ring formation causes abnormalities. {{Chromosomal abnormalities Ring chromosomes
A ring chromosome is an aberrant chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
whose ends have fused together to form a ring. Ring chromosomes were first discovered by Lilian Vaughan Morgan
Lilian Vaughan Morgan (''née'' Sampson; July 7, 1870 – December 6, 1952) was an American experimental biologist who made seminal contributions to the genetics of the fruit fly, ''Drosophila melanogaster'', which cemented its status as one ...
in 1926. A ring chromosome is denoted by the symbol ''r'' in human genetics and ''R'' in ''Drosophila
''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species ...
'' genetics. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, but they may also arise spontaneously during development.
Formation
In order for a chromosome to form a ring, both ends of the chromosome are usually missing, enabling the broken ends to fuse together. In rare cases, the telomeres
A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...
at the ends of a chromosome fuse without any loss of genetic material, which results in a normal phenotype.
Complex rearrangements, including segmental microdeletions and microduplications, have been seen in numerous ring chromosomes, providing important clues regarding the mechanisms of their formation.Mosaicism for r(X) and der(X)del(X)(p11.23)dup(X)(p11.21p11.22) Provides Insight into the Possible Mechanism of Rearrangement, ''Molecular Cytogenetics'' 2008, 1:16 Small supernumary rings can also form, resulting in a partial trisomy. Ring chromosomes are unstable during cell division and can form interlocking or fused rings.
Associated syndromes
Humangenetic disorder
A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...
s can be caused by ring chromosome formation. Although ring chromosomes are very rare, they have been found in all human chromosomes. Symptoms seen in patients carrying ring chromosomes are more likely to be caused by the deletion of genes in the telomeric regions of affected chromosomes, rather than by the formation of a ring structure itself.Nelson Textbook of Pediatrics, Chapter 81, 604-627 https://www.clinicalkey.com/#!/content/book/3-s2.0-B9781455775668000818?scrollTo=%23hl0003126 Almost all ring chromosome syndromes feature marked growth delay.
Ring chromosomes can be inherited or sporadic. Mosaicism is common and affects the severity of the condition. Location of fusion also affects severity due to loss of differing amounts of genetic material from the ends of chromosomes.
Disorders arising from the formation of a ring chromosome include:
See also
*Chromosome abnormalities
A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where ther ...
References
External links
Atlas of Genetics and Cytogenetics in Oncology and Haematology
explains HOW the ring formation causes abnormalities. {{Chromosomal abnormalities Ring chromosomes