Ring chromosome

Ring chromosome

A ring chromosome is a chromosome whose arms have fused together to form a ring. A ring chromosome is denoted by the symbol r. Ring chromosomes may form in cells following genetic damage by mutagens like radiation, they may also arise spontaneously during development.

Formation

Normally, the ends of a chromosome are lost, enabling the arms to fuse together. However, ring formation can also occur with only one end being lost. In rare cases, the telomeres at the ends of a chromosome fuse without any disappearing of material. [ [http://humrep.oxfordjournals.org/cgi/reprint/20/2/462 Mitotic and meiotic behaviour of a naturally transmitted ring Y chromosome: reproductive risk evaluation] Núria Arnedo, Carme Nogués, Mercè Bosch and Cristina Templado]

Associated diseases

Human genetic disorders can be caused by spontaneous ring chromosome formation; although ring chromosomes are very rare, they have been found in nearly all human chromosomes. Disorders arising from the formation of a ring chromosome include ring chromosome 20 syndrome where a ring formed by one copy of chromosome 20 is associated with epilepsy; ring chromosome 14 and ring chromosome 13 syndrome are associated with mental retardation and dysmorphic facial features; ring chromosome 15 is associated with mental retardation, dwarfism and microcephaly. Ring formation of an X-chromosome causes Turner syndrome. 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.

Complex rearrangements including segmental microdeletions and microduplications have been seen in numerous ring chromosomes providing important clues regarging the mechanisms of their formation [ [http://www.molecularcytogenetics.org/content/1/1/16 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] .

ee also

*Chromosome abnormalities

References

*Schmidt et al. 1981. Ring chromosome 14: a distinct clinical entity. "Journal of Medical Genetics" 18:304-307

References

External links

* [http://atlasgeneticsoncology.org/Deep/RingChromosID20030.html Atlas of Genetics and Cytogenetics in Oncology and Haematology] , explains HOW the ring formation causes abnormalities.


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См. также в других словарях:

  • ring chromosome — ring chromosome. См. кольцевая хромосома. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Ring chromosome — A structurally abnormal chromosome in which the end of each chromosome arm has been lost and the broken arms have been reunited in ring formation. A ring chromosome is denoted by the symbol r. * * * (r) a chromosome in which both ends have been… …   Medical dictionary

  • Ring chromosome 20 syndrome — Ring chromosome 20, ring shaped chromosome 20 or r(20) syndrome is a rare human chromosome abnormality where the two arms of chromosome 20 fuse to form a ring chromosome. The syndrome is associated with epileptic seizures, behaviour disorders and …   Wikipedia

  • Ring chromosome 18 syndrome — Infobox Disease Name = PAGENAME Caption = DiseasesDB = 32338 ICD10 = ICD9 = ICDO = OMIM = MedlinePlus = eMedicineSubj = eMedicineTopic = MeshID = Ring chromosome 18 syndrome is a rare condition in which one or both ends of chromosome 18 have been …   Wikipedia

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  • Chromosome 21 (human) — Chromosome 21 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. The trisomy of the 21st chromosome causes Down Syndrome. Chromosome 21 is the smallest human chromosome, 47 million nucleotides… …   Wikipedia

  • Chromosome 5 (human) — Chromosome 5 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 5 spans about 181 million base pairs (the building blocks of DNA) and represents almost 6% of the total DNA in cells.… …   Wikipedia

  • Chromosome 22 (human) — Chromosome 22 is one of the 23 pairs of chromosomes in human cells. Humans normally have two copies of Chromosome 22 in each cell. Chromosome 22 is the second smallest human chromosome, spanning about 49 million DNA base pairs and representing… …   Wikipedia

  • Chromosome — A visible carrier of the genetic information. The 3 billion bp (base pairs) in the human genome are organized into 24 distinct, physically separate microscopic units called chromosomes. All genes are arranged linearly along the chromosomes. The… …   Medical dictionary

  • Chromosome abnormality — The three major single chromosome mutations; deletion (1), duplication (2) and inversion (3) …   Wikipedia


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