![]() The shuffling of genes brought about by genetic recombination produces increased genetic variation. The crossover process leads to offspring having different combinations of genes from those of their parents, and can occasionally produce new chimeric alleles. ![]() In eukaryotes, recombination during meiosis is facilitated by chromosomal crossover. Thomas Hunt Morgan's illustration of crossing over (1916) V(D)J recombination in organisms with an adaptive immune system is a type of site-specific genetic recombination that helps immune cells rapidly diversify to recognize and adapt to new pathogens. Recombination can be artificially induced in laboratory ( in vitro) settings, producing recombinant DNA for purposes including vaccine development. Genetic recombination and recombinational DNA repair also occurs in bacteria and archaea, which use asexual reproduction. Gene conversion - the process during which homologous sequences are made identical also falls under genetic recombination. In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair. In meiosis, non-sister homologous chromosomes pair with each other so that recombination characteristically occurs between non-sister homologues. ![]() ![]() In meiosis and mitosis, recombination occurs between similar molecules of DNA ( homologous sequences). In this case, new combinations of alleles are not produced since the sister chromosomes are usually identical. Recombination may also occur during mitosis in eukaryotes where it ordinarily involves the two sister chromosomes formed after chromosomal replication. The information transfer may occur without physical exchange (a section of genetic material is copied from one chromosome to another, without the donating chromosome being changed) (see SDSA - Synthesis Dependent Strand Annealing pathway in Figure) or by the breaking and rejoining of DNA strands, which forms new molecules of DNA (see DHJ pathway in Figure). This may be followed by information transfer between the chromosomes. ĭuring meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. Most recombination occurs naturally and can be classified into two types: (1) int erchromosomal recombination, occurring through independent assortment of alleles whose loci are on different but homologous chromosomes (random orientation of pairs of homologous chromosomes in meiosis I) & (2) int rachromosomal recombination, occurring through crossing over. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be further passed on from parents to offspring. Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. ![]() Most recombination events appear to be the SDSA type. NCO recombinants are thought to occur primarily by the Synthesis Dependent Strand Annealing (SDSA) model, illustrated on the left, above. CO recombination is thought to occur by the Double Holliday Junction (DHJ) model, illustrated on the right, above. Repair of the gap can lead to crossover (CO) or non-crossover (NCO) of the flanking regions. A current model of meiotic recombination, initiated by a double-strand break or gap, followed by pairing with an homologous chromosome and strand invasion to initiate the recombinational repair process. ![]()
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