Gene conversion

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Under gene conversion is defined as a non-reciprocal exchanges of DNA sequences. During meiosis , a reciprocal exchange of DNA can occur between the same sections of chromatids as a result of crossing over twice and reconnecting the double strands ( crossing-over ). Thread 1 gets what thread 2 had and vice versa. This is not the case with gene conversion (non-reciprocal exchange), because a sequence is transferred to the other strand, but not vice versa.

There are 2 mechanisms for this:

1. via DNA heteroduplex : Instead of both DNA strands, only one strand is crossed and reconnected , but the other is lost. This leads to strand loss in the so-called donor sequence and mismatches in the acceptor sequence . Single strand losses and mismatches are then corrected by the cell's own repair mechanisms. In the case of the mismatch strand, the repair enzymes cannot differentiate between the original and the copy and may cut out the original and supplement the copy. This mechanism has been demonstrated in mammals .
Of course, it can also happen that there are mismatches on both sides. If the "originals" are then replaced both times, one speaks of an aberrant (= erroneous) 2: 2 ratio. If copies are replaced both times, there was ultimately no recombination. In the last two cases, however, one would not speak of gene conversion.

2. via cDNA intermediate: this mechanism requires a reverse transcriptase . This can transcribe any (any) mRNA into a cDNA . The cDNA can then integrate into the genome via homologous crossing-over and thus align similar genes or other gene copies. This path was discovered in the baker's yeast Saccharomyces cerevisiae . The transposable LINE elements are of particular importance in this mechanism . B. Copying exons from one gene to another (so-called exon shuffling ).


Gene conversion plays an important role in the evolution of gene families . It enables a concerted (joint) evolution of paralog genes. This happens when the intraspecies similarity is greater than the interspecies. With the cDNA mechanism, a concerted gene evolution can take place if the regulatory areas are not also doubled.

Of course, gene conversion is therefore also a mechanism for DNA repair that is used, for example, in double-strand breaks.


  • Bollag RJ, Elwood DR et al .: Formation of Heteroduplex DNA during Mammalian Chromosome Gene Conversion. In: Molecular and Cellular Biology. 12-4; Pp. 1546-1552; April 1992
  • Melamed C, Nevo J et al .: Involvement of cDNA in Homologous Recombination between Ty Elements in Saccharomyces cerevisiae. In: Molecular and Cellular Biology. 12-4; Pp. 1613-1620; April 1992