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recombination is thought to occur by the Double
Holliday Junction (DHJ) model, illustrated on the right, above. NCO recombinants are thought to occur primarily by the Synthesis Dependent Strand Annealing (SDSA) model, illustrated on the left, above. Most recombination events appear to be the SDSA type. At various steps of the recombination process, heteroduplex DNA (double-stranded DNA consisting of single strands from each of the two homologous chromosomes) is formed.
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203:(see Figure). One of these 3’ single stranded DNA segments then invades a homologous sequence on the homologous chromosome, forming an intermediate which can be repaired through different pathways resulting either in crossovers (CO) or noncrossovers (NCO) as illustrated in the Figure. By one pathway, a structure called a double
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which may or may not be perfectly complementary) is formed. During meiosis non-crossover recombinants occur frequently and these appear to arise mainly by the SDSA pathway. Non-crossover recombination events occurring during meiosis likely reflect instances of repair of DNA double-strand damages or
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enzyme makes staggered nicks in a pair of sister chromatid strands (in a tetrad organization of prophase). Subsequent enzymes trim back the 5' ends of the strand and a protein complex binds to the 3' single-stranded ends. Rad51 protein is recruited and binds in a protein complex to search for a
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A current model of meiotic recombination, initiated by a double-strand break or gap, followed by pairing with a homologous chromosome and strand invasion to initiate the recombinational repair process. Repair of the gap can lead to crossover (CO) or non-crossover (NCO) of the flanking regions. CO
276:"Meiotic versus mitotic recombination: two different routes for double-strand break repair: the different functions of meiotic versus mitotic DSB repair are reflected in different pathway usage and different outcomes"
211:, there is information exchange but not physical exchange. At various steps of these recombination processes, heteroduplex DNA (double-stranded DNA consisting of single strands from each of the two
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pathway for repairing DNA double-strand breaks appears to be the SDSA pathway (rather than the DSBR pathway). The SDSA pathway produces non-crossover recombinants (see Figure).
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complementary sequence analogous to double-strand-break repair. The filament searches for the homologous chromosome, strand invasion occurs where the new chromosome forms a
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other types of DNA damages. When mismatches occur in heteroduplex DNA, the sequence of one strand can be repaired to bind the other strand with perfect complementarity.
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analyses. Another is the heteroduplexes formed when non-natural analogs of nucleic acids are used to bind with nucleic acids; these heteroduplexes result from performing
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that when cut in a transversal pattern by endonucleases form 2 heteroduplex strand products.
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over the bottom sister chromatid, then the ends are annealed. This process can yield double
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One such example is the heteroduplex DNA strand formed in
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143:of single complementary strands derived from
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274:Andersen SL, Sekelsky J (December 2010).
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250:Heteroduplex DNA is also a source of
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323:Allers T, Lichten M (July 2001).
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193:Meiotic recombination
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