Gene conversion
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2008-07-16T09:53:44Z
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/* Importance of gene conversion in the cohesiveness of the gene pool */
[[Image:Conversion and crossover.jpg|thumb|right|300px|The difference between '''gene conversion''' and [[chromosomal crossover]]. Blue are the two [[chromatid]]s of one chromosome and red are the two chromatids of another one.]]
'''Gene conversion''' is an event in DNA [[genetic recombination]], which occurs during [[meiosis|meiotic]] division. It is a process by which DNA sequence information is transferred from one DNA helix (which remains unchanged) to another DNA helix, whose sequence is altered.
It is one of the ways a gene may be mutated. Gene conversion may lead to [[non-Mendelian inheritance]] and has often been recorded in fungal crosses.<ref>Stacey, K. A. 1994. Recombination. In: Kendrew John, Lawrence Eleanor (eds.). ''The Encyclopedia of Molecular Biology''. Oxford: Blackwell Science, 945–950.</ref>
==Mechanism==
This conversion of one allele to the other is due to inappropriate base mismatch repair during recombination: if one of the four strands during meiosis pairs up with one of the four strands of a different [[chromosome]], as can occur if there is sequence [[homology (biology)|homology]], mismatch repair can alter the sequence of one of the chromosomes, so that it is identical to the other.
Gene conversion can result from the repair of damaged DNA as described by the Double Strand Break Repair Model. Here a break in both strands of DNA is repaired off an intact homologous region of DNA. Resection (degradation) of the DNA strands near the break site leads to stretches of single stranded DNA that can invade the homologous DNA strand. The intact DNA can then function as a template to copy the lost DNA. During this repair process a structure called a double [[Holliday junction|Holliday structure]] is formed. Depending on how this structure is resolved (taken apart) either cross-over or gene conversion products result.
==Effect==
Normally, an organism that has inherited different copies of a gene from each of its parents is called heterozygous. This is generically represented as genotype: Aa (i.e. one copy of variant ([[allele]]) 'A', and one copy of allele 'a'). When a heterozygote creates gametes by [[meiosis]], the alleles normally split, and end up in a 1:1 ratio in the resulting cells. However, in gene conversion, the ratio becomes other than the expected 1A:1a is observed, in which A and a are the two alleles. Such examples are 3A:1a, 1A:3a, 5A:3a or 3A:5a. In other words, there can for example be three times as many A alleles than a alleles expressed in the daughter cells, as is the case in 3A:1a.
==Importance of gene conversion in the cohesiveness of the gene pool==
Gene conversion acts to ''homogenize'' the DNA sequences composing the [[gene pool]] of a species.<ref>Kull, Kalevi 2000. Organisms can be proud to have been their own designers. ''Cybernetics and Human Knowing'' 7(1): 45–55.[[http://www.zbi.ee/~kalevi/chkfin.htm]]</ref> Every gene conversion event takes as its substrate two DNA sequences that are homologous but not identical, because of sequence mismatches and yields two identical DNA sequences. Gene conversion forms the cohesive force that links DNA sequences within different organisms of a [[species]]. Over time, gene conversion events yield a homogenous set of DNA sequences, both for [[Allele|allelic]] forms of a gene and for [[Gene family|multi gene families]]. [[Interspersed repeat]]s act to break up this linkage and catalyze the formation of novel genes during evolution.
==References==
<references/>
==External links==
* {{MeshName|Gene+conversion}}
* images: http://www.web-books.com/MoBio/Free/Ch8D4.htm and http://www.web-books.com/MoBio/Free/Ch8D2.htm
[[Category:Genetics]]
[[Category:Molecular evolution]]
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{{Genetic recombination}}
{{MolecularEvolution}}