Gene conversion

With a non-reciprocal gene conversion is meant the exchange of DNA sequences. During mitosis and meiosis can occur between the same sections of chromatids by twice crosses and relink the respective duplexes ( crossing-over ) for the reciprocal exchange of DNA. Line 1 gets what train 2 had and vice versa. When gene conversion, however, is not the case ( non-reciprocal exchange), because a sequence is transferred to the other, but not vice versa.

There are two possible mechanisms for this:

1 by DNA heteroduplex: Instead of both DNA strands only one strand is crossed and re-linked, but the other is lost. Thus it comes to strand loss in the so-called donor sequence and mismatches in the acceptor. Single-strand losses and mismatches are then corrected by the cell's own repair mechanisms. When the mismatch strand repair enzymes can not distinguish between original and copy, and possibly cut the original out and complete the copy. This mechanism has been shown in mammals. Of course, it can also happen that there is on both sides to mismatches. Then be replaced both times the "originals", as one speaks of a aberrant ( = mistaken ) 2:2 ratio. If both times copies replaced, so there was ultimately no recombination. In the last two cases, one would not speak of gene conversion.

2 by cDNA intermediate: In this mechanism, a reverse transcriptase is required. This can rewrite a (any ) mRNA into a cDNA. The cDNA can integrate into the genome and thus align similar genes or other gene copies then homologous crossing-over. This way it has been discovered in the baker yeast Saccharomyces cerevisiae. Of particular importance in this mechanism also have the LINE transposable elements, such as the Can copy exons of a gene in another (so-called exon shuffling).

Importance

Gene conversion plays an important role in the evolution of gene families. It allows a concerted ( common ) Evolution of paralogous genes. This happens when the intraspecific similarity is greater than the interspecific. When cDNA mechanism can be a concerted gene evolution, when the regulatory regions are not mitverdoppelt.

Of course, gene conversion is thus also a mechanism for DNA repair, which takes place approximately at double-strand breaks using.