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ru>Natg 19: Disambiguate Silencing to Gene silencing using popups

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Disambiguate Silencing to Gene silencing using popups

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'''Reciprocal silencing''', a [[Genetics|genetic]] phenomenon that primarily occurs in plants, refers to the pattern of redundant [[genes]] being [[gene silencing|silenced]] following a [[polyploidy|polyploid]] event. Polyploidy (wholesale [[genome]] duplication) is common in [[plants]] and constitutes an important method of speciation.<ref name= "Werth">Werth, C. and M. Whindam (1991) A Model for Divergent, Allopatric Speciation of Polyploid Pteridophytes Resulting from Silencing of Duplicate Gene Expression. American Naturalist 137: 515-526</ref> When a [[polyploid]] species arises, its [[genome]] contains [[homoeology|homoeologs]], duplicated [[chromosomes]] with equivalent genetic information. However silencing of redundant genes occurs rapidly in new polyploids through genetic and [[epigenetic]] means. This primarily occurs because redundancy allows one of the two genes present for each locus to be silenced without affecting the [[phenotype]] of the organism, and thus [[mutations]] that eliminate [[gene expression]] are much less likely to be deleterious or lethal.<ref name="Werth"/><ref name="Pikaard">Pikaard, C. S (2001) Genomic change and gene silencing in polyploids. Trends in Genetics 12:675-677</ref> This allows mutations that would be lethal in diploid populations to accumulate in polyploids. Reciprocal silencing refers to the specific pattern of silencing where equivalent loci in are both silenced and expressed in a reciprocal manner. This phenomenon is observed on two distinct scales.

==Reciprocal silencing between populations ==
[[Allopolyploids]] are species whose increased complement of genetic material is the result of hybridization of two closely related [[species]]. Thus homeologous chromosomes in allopolyploids are equivalent, but not identical. These differences mean that the precise pattern of [[gene silencing|silencing]] and expression can have important [[phenotypic]] effects. Reciprocal silencing on the [[population]] level refers to the case where two populations are each descended from the same [[allopolyploid]]. In one population, one of the two equivalent loci (A) is expressed while the other (B) has been silenced, while in the other population the reciprocal pattern occurs, with B being expressed and A silenced. It is important to note that this refers to equivalent loci, specific locations within the genome, rather than the entire homeologous [[chromosome]].

Reciprocal silencing on the population level has been proposed as a means of [[allopatric speciation]] following a [[polyploidy|polyploid]] event.<ref name="Werth" /> Allopatric speciation occurs when two populations of the same species become spatially separated and accumulate enough genetic differences to lose the ability to interbreed. As redundant genes are silenced in allopolyploids there is the potential for rapid genetic differences to accumulate through reciprocal silencing. These differences can lead to the loss of ability to interbreed between separated populations at a faster rate than other methods of [[speciation]], given the relative speed with which genes are silenced following a polyploid event. Faster still, redundant genes can be silenced through [[epigenetic]] means, although the importance of this phenomenon is not fully understood.<ref name= "Pikaard" />

==Reciprocal silencing between tissues==
Reciprocal silencing on the [[Tissue (biology)|tissue]] level refers to the same pattern of [[Gene silencing|silencing]] and expression of homeologous loci. However, in this case, the differences in silencing and expression occur between two types of tissue within the same individual, rather than in individuals of different populations. This is an example of [[neofunctionalization]], a process where duplicated genes that were once at equivalent loci evolve to carry out two separate functions.<ref>Chaudhary, B. Flagel, L. Stupar, R. Udal, J. Verma, N. Springer, N. and J. F. Wendel (2009) Reciprocal Silencing, Transcriptional Bias and Functional Divergens of Homeologs in Polyploid Cotton (Gossypium). Genetics 183: 503-517</ref> Since different tissues require different genes to be expressed, reciprocal silencing can occur between [[Tissue (biology)|tissue]]s. Importantly, while the pattern of gene expression is the same as in the population case, the genetic means by which this pattern is achieved are very different. While [[silencing mutations]] are thought to be the main source of reciprocal silencing
at the population level, at the [[Tissue (biology)|tissue]] level only epigenetic factors are in play, since expressible copies of both homeologous loci must exist in all cells in an individual if different tissues express different homeologs.

== References ==
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[[Category:Genetics]]
[[Category:Gene expression]]

Reciprocal silencing - История изменений

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ru>Natg 19: Disambiguate Silencing to Gene silencing using popups