Robertsonian translocation
Robertsonian translocation (ROB) is a
Mechanism
All chromosomes in animals have a long arm (known as q) and a short arm (known as p), separated by a region called the
This type of translocation may involve
Consequences
In humans, when a Robertsonian translocation joins the long arm of chromosome 21 with the long arm of chromosomes 14 or 15, the
A Robertsonian translocation in balanced form results in no excess or deficit of genetic material and causes no health difficulties. In unbalanced forms, Robertsonian translocations cause chromosomal deletions or addition and result in syndromes of multiple malformations, including trisomy 13 (Patau syndrome) and trisomy 21 (Down syndrome). The most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, 14 and 21, and 14 and 15.[2]
A Robertsonian translocation results when the long arms of two acrocentric chromosomes fuse at the centromere and the two short arms are lost. If, for example, the long arms of chromosomes 13 and 14 fuse, no significant genetic material is lost—and the person is completely normal in spite of the translocation. Common Robertsonian translocations are confined to the acrocentric chromosomes 13, 14, 15, 21 and 22, because the short arms of these chromosomes encode for
Most people with Robertsonian translocations have only 45 chromosomes in each of their cells, yet all essential genetic material is present, and they appear normal. Their children, however, may either be normal, carry the fusion chromosome (depending which chromosome is represented in the gamete), or they may inherit a missing or extra long arm of an acrocentric chromosome (phenotype affected). Genetic counseling and genetic testing is offered to families that may be carriers of chromosomal translocations.[12]
Rarely, the same translocation may be present homozygously if heterozygous parents with the same Robertsonian translocation have children. The result may be viable offspring with 44 chromosomes.[13] Outside of humans, Przewalski's horse has 66 chromosomes, while both of domesticated horses and the tarpan have 64 chromosomes and donkeys have 62; it is thought that the difference is due to a Robertsonian translocation.[6]
Nomenclature
The
Name
Robertsonian translocations are named after the American
References
- ^ E. Therman, B. Susman and C. Denniston. The nonrandom participation of human acrocentric chromosomes in Robertsonian translocations. Annals of Human Genetics 1989;53:49-65.
- ^ a b "Unique: Rare Chromosome Disorder Support Group" (PDF). Archived from the original (PDF) on 2019-02-18. Retrieved 2019-02-17.
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- ^ More details under Mule and Hinny.
- ^ ISBN 978-1-118-52212-7.
- ^ a b Robertson WRB. Chromosome studies. I. Taxonomic relationships shown in the chromosomes of Tettigidae and Acrididae. V-shaped chromosomes and their significance in Acrididae, Locustidae and Gryllidae: chromosome and variation. J Morph 1916;27:179-331.
- ISBN 978-0-07-352526-6.
- ^ Peter J. Russel; Essential Genetics 2003
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- ^ "ISCN Symbols and Abbreviated Terms". Coriell Institute for Medical Research. Retrieved 2022-10-27.
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- S2CID 11712171.