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List of chromosomal translocations: Wikis

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Chromosomal translocation of the 4th and 20th chromosome.

In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A fusion gene may be created when the translocation joins two otherwise separated genes, an event which is common in cancer. It is detected on cytogenetics or a karyotype of affected cells. There are two main types, reciprocal (also known as non-Robertsonian) and Robertsonian. Also, translocations can be balanced (in an even exchange of material with no genetic information extra or missing, and ideally full functionality) or unbalanced (where the exchange of chromosome material is unequal resulting in extra or missing genes).

Contents

Reciprocal (non-Robertsonian) translocations

Reciprocal translocations are usually an exchange of material between nonhomologous chromosomes. They are found in about 1 in 625 human newborns.[1] Such translocations are usually harmless and may be found through prenatal diagnosis. However, carriers of balanced reciprocal translocations have increased risks of creating gametes with unbalanced chromosome translocations leading to miscarriages or children with abnormalities. Genetic counseling and genetic testing is often offered to families that may carry a translocation.

Robertsonian translocations

This type of rearrangement involves two acrocentric chromosomes that fuse near the centromere region with loss of the short arms. The resulting karyotype in humans leaves only 45 chromosomes since two chromosomes have fused together. Robertsonian translocations have been seen involving all combinations of acrocentric chromosomes. The most common translocation in human involves chromosomes 13 and 14 and is seen in about 0.97 / 1000 newborns.[2] Like other translocations, carriers of Robertsonian translocations are phenotypically normal, but there is a risk of unbalanced gametes which lead to miscarriages or abnormal offspring. For example, carriers of Robertsonian translocations involving chromosome 21 have a higher chance to have a child with Down syndrome.This case of translocation is called trisomy by translocation. The main cause (more than 95%) is explained by a mis-segragation (Nondisjunction) during gamatogenesis. The mother has more risk of transmission than the father.

Some human diseases caused by translocations are:

By chromosome

Overview of chromosomal translocations involved in different cancers, as well as implicated in some other conditions, e.g. schizophrenia[3], with chromosomes arranged in standard karyogram order. Abbreviations:
ALL - Acute lymphoblastic leukemia
AML - Acute myeloid leukemia
CML - Chronic myelogenous leukemia
DFSP - Dermatofibrosarcoma protuberans
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Denotation

The International System for Human Cytogenetic Nomenclature (ISCN) is used to denote a translocation between chromosomes.[4] The designation t(A;B)(p1;q2) is used to denote a translocation between chromosome A and chromosome B. The information in the second set of parentheses, when given, gives the precise location within the chromosome for chromosomes A and B respectively—with p indicating the short arm of the chromosome, q indicating the long arm, and the numbers after p or q refers to regions, bands and subbands seen when staining the chromosome with a staining dye. See also the definition of a genetic locus.

Examples

History

In 1938 Karl Sax, at the Harvard University Biological Laboratories, published a paper entitled "Chromosome Aberrations Induced by X-rays," which demonstrated that radiation could induce major genetic changes by affecting chromosomal translocations. The paper is thought to mark the beginning of the field of radiation cytology, and led him to be called "the father of radiation cytology".

See also

References

  1. ^ M. Oliver-Bonet; J. Navarro1, M. Carrera, J. Egozcue, J. Benet (October 2002). "Aneuploid and unbalanced sperm in two translocation carriers: evaluation of the genetic risk". Molecular Human Reproduction (Oxford University Press for the European Society for Human Reproduction and Embryology) 8 (10): 958–963. doi:10.1093/molehr/8.10.958. ISSN 1460-2407. PMID 12356948. http://molehr.oxfordjournals.org/cgi/content/full/8/10/958?ijkey=e61cf0fc0c0b4228aa0188dc434b99ffa9625359. Retrieved 2008-12-26. 
  2. ^ E. Anton; J. Blanco, J. Egozcue, F. Vidal (April 29, 2004). "Sperm FISH studies in seven male carriers of Robertsonian translocation t(13;14)(q10;q10)". Human Reproduction (Oxford University Press) 19 (6): 1345–1351. doi:10.1093/humrep/deh232. ISSN 1460-2350. PMID 15117905. http://humrep.oxfordjournals.org/cgi/content/full/19/6/1345. Retrieved 2008-12-25. 
  3. ^ a b Semple CA, Devon RS, Le Hellard S, Porteous DJ (April 2001). "Identification of genes from a schizophrenia-linked translocation breakpoint region". Genomics 73 (1): 123–6. doi:10.1006/geno.2001.6516. PMID 11352574. 
  4. ^ Schaffer, Lisa. (2005) International System for Human Cytogenetic Nomenclature S. Karger AG ISBN 978-3805580199

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