31-08-2017, 11:48 AM
Gene conversion is the process by which a DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event. Gene conversion may be allelic, which means that one allele of the same gene replaces another allele, or ectopic, meaning that one paralogous DNA sequence converts to another.
Conversion from one allele to another is often due to repair of the mismatch in homologous recombination: if one of the four chromatids during meiosis is paired with another chromatid, as may occur due to sequence homology, the Transfer of the DNA strand may occur. This can alter the sequence of one of the chromosomes, so that it is identical to the other.
The meiotic recombination is initiated through the formation of a double strand break (DSB). The 5 'ends of the tear are then degraded, leaving long 3' protrusions of several hundred nucleotides. One of these 3 'single-stranded DNA segments then invades a homologous sequence on the homologous chromosome, forming an intermediate that can be repaired through different pathways resulting in either crossovers (CO) or noncrossovers (NCO). At various stages of the recombination process, heteroduplex DNA is formed (double-stranded DNA consisting of individual strands of each of the two homologous chromosomes which may or may not be perfectly complementary). When mismatches occur in the heteroduplex DNA, the sequence of one strand will be repaired to join the other strand with perfect complementarity, leading to the conversion from one sequence to another. This repair process may follow any two alternative routes as illustrated in the figure. By one route, a structure called double bonding of Holliday (DHJ) is formed, which leads to the exchange of DNA strands. On the other hand, called Synthesis Dependent Chain Recovery (SDSA), there is information exchange but not physical exchange. Gene conversion will occur during SDSA if the two DNA molecules are heterozygous at the site of recombination repair. Gene conversion may also occur during recombination repair involving DHJ, and this gene conversion may be associated with the physical recombination of the DNA duplexes on both sides of the DHJ.
Conversion from one allele to another is often due to repair of the mismatch in homologous recombination: if one of the four chromatids during meiosis is paired with another chromatid, as may occur due to sequence homology, the Transfer of the DNA strand may occur. This can alter the sequence of one of the chromosomes, so that it is identical to the other.
The meiotic recombination is initiated through the formation of a double strand break (DSB). The 5 'ends of the tear are then degraded, leaving long 3' protrusions of several hundred nucleotides. One of these 3 'single-stranded DNA segments then invades a homologous sequence on the homologous chromosome, forming an intermediate that can be repaired through different pathways resulting in either crossovers (CO) or noncrossovers (NCO). At various stages of the recombination process, heteroduplex DNA is formed (double-stranded DNA consisting of individual strands of each of the two homologous chromosomes which may or may not be perfectly complementary). When mismatches occur in the heteroduplex DNA, the sequence of one strand will be repaired to join the other strand with perfect complementarity, leading to the conversion from one sequence to another. This repair process may follow any two alternative routes as illustrated in the figure. By one route, a structure called double bonding of Holliday (DHJ) is formed, which leads to the exchange of DNA strands. On the other hand, called Synthesis Dependent Chain Recovery (SDSA), there is information exchange but not physical exchange. Gene conversion will occur during SDSA if the two DNA molecules are heterozygous at the site of recombination repair. Gene conversion may also occur during recombination repair involving DHJ, and this gene conversion may be associated with the physical recombination of the DNA duplexes on both sides of the DHJ.