geneconversion

Gene conversion is a non-reciprocal genetic exchange in which a DNA sequence on one chromosome or DNA molecule is copied from a homologous sequence on another chromosome or molecule, resulting in the recipient sequence becoming identical to the donor sequence. Unlike standard recombination, gene conversion does not involve an equal exchange of flanking genetic material.

The process typically occurs during homologous recombination or DNA repair. A region of DNA on the recipient aligns with a homologous donor region, forming a heteroduplex that may contain mismatches. The mismatch repair system or DNA synthesis then uses the donor sequence as a template, replacing the recipient's bases and creating a conversion tract that changes one allele to match the donor. The tract length varies from a few bases to several kilobases.

Gene conversion plays a role during meiosis in many organisms and can also occur during mitotic DNA repair. In yeast, Saccharomyces cerevisiae mating-type switching is driven by gene conversion using donor loci to replace the active MAT locus. In bacteria and other organisms, conversion can occur during transformation, transduction, or repair of double-strand breaks, contributing to allelic diversity.

Gene conversion can bias inheritance and affect evolutionary trajectories by transferring sequence information without reciprocal exchange. It can influence gene family evolution, immune receptor diversification in some vertebrates, and the maintenance of identity among repetitive sequences. Detection relies on comparative sequencing and SNP analysis at polymorphic loci; non-reciprocal sequence transfer without a corresponding change in flanking regions is characteristic.