Robertsonian translocation: Difference between revisions

[[File:Robertsonian translocation.png|thumb|A Robertsonian translocation. The short arms of the chromosomes (shown on right) are often lost ]]

'''Robertsonian translocation''' ('''ROB''') is a [[Chromosome abnormality|chromosomal abnormality]] whereinwhere the entire long arms of two of a certain type of adifferent [[chromosome]] called an [[acrocentric chromosome|chromosomes]] become fused to each other. It is the most common form of [[chromosomal translocation]] in humans, affecting 1 out of every 1,000 babies born.<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> It does not usually cause directmedical health difficultiesproblems, howeverthough suchsome personspeople aremay almostproduce always[[Gamete|gametes]] infertilewith becausean theirincorrect chromosomenumber countof doeschromosomes, notresulting matchin thata risk of most humansmiscarriage. In rare cases this [[geneticChromosomal disorderstranslocation|translocation]] results in [[Down syndrome]] and [[Patau syndrome]].<ref name=":1">{{Cite web |url=https://www.rarechromo.org/media/information/Other/Robertsonian%20Translocations%20FTNW.pdf |title=Unique: Rare Chromosome Disorder Support Group |access-date=2019-02-17 |archive-date=2019-02-18 |archive-url=https://web.archive.org/web/20190218082031/https://www.rarechromo.org/media/information/Other/Robertsonian%20Translocations%20FTNW.pdf |url-status=dead }}</ref> Robertsonian translocations result in a reduction in the number of chromosomes. A Robertsonian evolutionary fusion, which may have occurred in the common ancestor of humans and other [[Great Apes|great apesape]]s, is the reason humans have 46 chromosomes while all other primates have 48. Detailed DNA studies of [[chimpanzee]], [[orangutan]], [[gorilla]] and [[bonobo]] [[ape]]s has determined that where [[human]] [[Chromosomechromosome 2]] is present in our DNA in all four great apes this is split into two separate chromosomes typically numbered 2a and 2b.<ref name="pmid28333343">{{cite journal |last1=Chiatante |first1=Giorgia |last2=Giannuzzi |first2=Giuliana |last3=Calabrese |first3=Francesco Maria |last4=Eichler |first4=Evan E. |last5=Ventura |first5=Mario |title=Centromere Destiny in Dicentric Chromosomes: New Insights from the Evolution of Human Chromosome 2 Ancestral Centromeric Region |journal=[[Molecular Biology and Evolution]] |date=1 July 2017 |volume=34 |issue=7 |pages=1669–1681 |doi=10.1093/molbev/msx108 |pmid=28333343 |url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5722054/ |access-date=25 June 2023 |pmc=5722054}}</ref><ref name="pmid25984837">{{cite journal |last1=Pratas |first1=Diogo |last2=Silva |first2=Raquel M. |last3=Pinho |first3=Armando J. |last4=Ferreira |first4=Paulo J.S.G. |title=An alignment-free method to find and visualise rearrangements between pairs of DNA sequences |journal=[[Scientific Reports]] |date=18 May 2015 |volume=5 |issue=1 |pages=1203 |doi=10.1038/srep10203 |pmid=25984837 |urlpmc=https://www4434998|bibcode=2015NatSR.ncbi.nlm.nih.gov/pmc/articles/PMC4434998/510203P |access-date=25 June 2023 |pmc=4434998}}</ref> Similarly, the fact that horses have 64 chromosomes and donkeys 62, and that they can still have common, albeit usually infertile, offspring,<ref>More details under [[Mule]] and [[Hinny]].</ref> may be due to a Robertsonian evolutionary fusion at some point in the descent of today's donkeys from their common ancestor.<ref name="equus" />

HumansAll chromosomes in animals have 5a long arm (known as ''q'') and a short arm (known as ''p''), separated by a region called the [[autosomalcentromere]]. Robertsonian translocations can only occur between [[chromosomes]] withwhich armshave thatthe arecentromere particularlyvery discordantclose into lengthone end. This means these chromosomes have a long arm which is particularly long, and a short arm which is particularly short. These are known as [[Centromere#Acrocentric|acrocentric]] chromosomes. TheseHumans arehave five of these acrocentric chromosomes: [[Chromosome 13 (human)|13]], [[Chromosome 14 (human)|14]], [[Chromosome 15 (human)|15]], [[Chromosome 21 (human)|21]] and [[Chromosome 22 (human)|22]]. When these chromosomes break at their [[centromere]]s, the two resulting long arms may fuse. The result is a single, large chromosome with a [[Centromere#Metacentric|metacentric]] centromere. This form of rearrangement is a Robertsonian translocation.{{citation needed|date=May 2022}}

This type of translocation may involve [[Homologous chromosome|homologous]] (paired) or non-homologous chromosomes. Owing to the acrocentric nature of the chromosomes involved, the long arms of these chromosomes contain the majority of genetic material contained on the original chromosomes. The short arms also join to form a smaller reciprocal product, which typically contains only nonessential genes also present elsewhere in the genome, and is usually lost within a few [[cell division]]s. This type of translocation is [[Cytology|cytologically]] visible, and can reduce chromosome number (in humans, from 23 to 22). However, the smaller chromosome carries so few essential genes that its loss is usually clinically insignificant.<ref name=":0">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.''</ref><ref>{{Cite book|title = Genetics From Genes to Genomes, 4e|last1 = Hartwell|first1 = Leland|publisher = McGraw-Hill|year = 2011|isbn = 978-0-07-352526-6|location = New York|pages = 443, 454|last2 = Hood|first2 = Leroy|last3 = Goldberg|first3 = Michael|last4 = Reynolds|first4 = Ann|last5 = Silver|first5 = Lee}}</ref>

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 [[Chromosomal translocation|unbalanced]] [[trisomy]] 21, causing [[Down syndrome]].<ref>{{Cite journal |last=Plaiasu |first=Vasilica |date=September 2017 |title=Down Syndrome - Genetics and Cardiogenetics |url=https://pubmed.ncbi.nlm.nih.gov/29218069/ |journal=Maedica |volume=12 |issue=3 |pages=208–213 |issn=1841-9038 |pmc=5706761 |pmid=29218069}}</ref>

AboutA oneRobertsonian translocation in abalanced thousandform newbornsresults havein ano Robertsonianexcess translocation.<ref>E.or Therman,deficit B.of Susmangenetic material and C.causes no health Dennistondifficulties. TheIn nonrandomunbalanced participationforms, ofRobertsonian humantranslocations acrocentriccause chromosomeschromosomal indeletions Robertsonianor translocations.addition ''Annalsand result in syndromes of Humanmultiple Genetics''malformations, 1989;53:49-65including trisomy 13 ([[Patau syndrome]]) and trisomy 21 ([[Down syndrome]]).</ref> The most frequent forms of Robertsonian translocations are between chromosomes 13 and 14, 14 and 21, and 14 and 15.<ref name=":1" />

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>{{Cite journal |last=Yip |first=Moh-Ying |date=April 2014 |title=Uniparental disomy in Robertsonian translocations: strategies for uniparental disomy testing |url=https://tp.amegroups.org/article/view/3546 |journal=Translational Pediatrics |language=en |volume=3 |issue=2 |pages=9807–9107 |doi=10.3978/j.issn.2224-4336.2014.03.03 |pmid=26835328 |pmc=4729106 |issn=2224-4344}}</ref><ref>{{Cite journal |last=Slijepcevic |first=Predrag |date=1998-05-01 |title=Telomeres and mechanisms of Robertsonian fusion |url=https://doi.org/10.1007/s004120050289 |journal=Chromosoma |language=en |volume=107 |issue=2 |pages=136–140 |doi=10.1007/s004120050289 |pmid=9601982 |s2cid=11712171 |issn=1432-0886}}</ref>