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The double strand break model of meiotic recombination allows for unequal amounts of heteroduplex DNA either side of the initial site of recombination, explaining some results that the Meselson-Radding model of recombination does not.

  1. Firstly, a double strand break is made in one chromosome (hence the name)
    
    aaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  2. A 5' to 3' nuclease digests back along each strand of the duplex until it hits a chi site.
    
    aaaaaa        aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaaa          aaaaaaaaaaaaaaaaaaaa
    
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  3. RecA mediated invasion of chromosome 2 by one of the strands of chromosome 1 occurs.
    aaaaaa       aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaa   bbbb          aaaaaaaaaaaaaaaaaaa
          \ /    \ 
           X      \
          / \      \
    bbbbbb   aaaa   bbbbbbbbbbbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  4. Strand A is extended with new DNA, which is represented by c (but note that c is identical to b - this is just to show the new DNA being produced). This displaces b, which continues to transfer over to the other chromosome.
    
    aaaaaa       aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaa   bbbbbbbbbbbbb aaaaaaaaaaaaaaaaaaa
          \ /             \
           X               \
          / \               \
    bbbbbb   ccccccccccccc   bbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  5. New DNA is synthesised to fill the gap on chromosome 1 (represented by d, but identical to b)
    
    aaaaaadddddddaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaa   bbbbbbbbbbbbb   aaaaaaaaaaaaaaaaa
          \ /             \ /
           X               X
          / \             / \
    bbbbbb   ccccccccccccc   bbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  6. Due to the two junctions, there are too many possible outcomes to describe trivially. When comparing to other types of meiotic recombination, note the differing amounts of heteroduplex DNA on the two chromosomes.

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