遺伝子変換

Gene conversion is a process where one DNA sequence is replaced by a highly similar sequence from a homologous chromosome, resulting in non-reciprocal exchange of genetic material. Unlike homologous recombination and strand invasion, which typically involve reciprocal exchange between two DNA molecules, gene conversion produces asymmetrical outcomes where one allele is converted to match another without equivalent reciprocal change.

Gene conversion increases genetic diversity by creating new allelic combinations without requiring crossing over. This mechanism allows cells to generate variation through localized sequence replacement, contributing to genomic stability while maintaining genetic flexibility. The process is particularly important in regions with repetitive sequences where multiple similar templates exist.

Gene conversion facilitates DNA repair by using homologous sequences as templates to restore damaged regions. When double-strand breaks or other lesions occur, the cell can employ gene conversion to replace corrupted sequences with intact copies from sister chromatids or homologous chromosomes, ensuring accurate restoration of genetic information.

Gene conversion requires recombination proteins including RAD51, which catalyzes strand invasion and homology search, along with nucleases and helicases that process DNA ends. These proteins work together to identify homologous sequences, facilitate strand exchange, and resolve recombination intermediates, ensuring accurate conversion of one DNA sequence to match its homolog.

Gene conversion corrects mismatches and ensures proper chromosome pairing during meiosis by converting one allele to match its homolog. This process reduces genetic conflicts between homologous chromosomes and prevents the propagation of mutations, thereby maintaining genomic stability across generations while allowing controlled genetic recombination.

Gene conversion and mismatch repair both address sequence discrepancies but operate differently. Mismatch repair corrects errors introduced during DNA replication by identifying and removing incorrect bases. Gene conversion, by contrast, replaces entire sequence segments with homologous templates, serving as a broader mechanism for maintaining sequence fidelity and genetic consistency.

Gene conversion occurs in both meiotic and mitotic cells, though with different frequencies and consequences. In somatic cells, mitotic gene conversion can generate genetic diversity within tissues and may contribute to immune system diversity. Uncontrolled gene conversion in somatic cells can occasionally lead to loss of heterozygosity or altered gene expression patterns.