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==Consequences==
In humans, when a Robertsonian translocation joins the long arm of chromosome 21 with the long arm of chromosomes 14 or 15, the [[heterozygous]] carrier is [[phenotype|phenotypically]] normal because there are two copies of all major chromosome arms and hence two copies of all essential genes.<ref>Peter J. Russel; Essential Genetics 2003</ref> However, the progeny of this carrier may inherit an unbalanced [[trisomy]] 21, causing [[Down syndrome]].<ref>{{
About one in a thousand newborns have a Robertsonian translocation.<ref>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.</ref> The most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, 14 and 21, and 14 and 15.<ref name=":1"/>
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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 [[rRNA]] which is present in multiple copies.<ref>{{cite journal | pmid= | volume= |title=Recombination between heterologous human acrocentric chromosomes | year=2022 |vauthors= Guarracino A, Buonaiuto S, Potapova T, Rhie A, Koren S, Rubinstein B, Fischer C, Gerton J, Phillippy A, Colonna V, Garrison E | journal=bioRxiv| doi=10.1101/2022.08.15.504037| s2cid= 251647679}}</ref>
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).
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.<ref>{{cite journal| pmid=6510025 | volume=38 | title=Homozygosity for a Robertsonian translocation (13q14q) in three offspring of heterozygous parents | year=1984 |vauthors=Martinez-Castro P, Ramos MC, Rey JA, Benitez J, Sanchez Cascos A | journal=Cytogenet Cell Genet | issue=4 | pages=310–2 | doi=10.1159/000132080}}</ref> Outside of humans,
==Nomenclature==
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== Name ==
Robertsonian translocations are named after the American [[zoologist]] and [[cytogeneticist]] [[William Rees Brebner Robertson]] (1881–1941) who first described a Robertsonian translocation in [[caelifera|grasshopper]]s in 1916.<ref name=":0" /> They are also called ''whole-arm translocations'' or ''centric-fusion translocations''.<ref>{{
==References==
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