The Meselson-Radding model of meiotic recombination explains how the regions of heteroduplex DNA on both sides of the initial recombination event are not necessarily the same length, providing an advantage over the Holiday model of recombination.
  1. Firstly, a nick is made in one strand of one of the chromosomes (in the following, each line represents a single strand of a double helix)
    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaa aaaaaaaaaaaaaaaaaaaaaaaaaa
    
    
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  2. Secondly, a new strand is produced, displacing the original one on one side of the nick (the new strand is represented by c, but is identical to a)
    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaaccccccccccc aaaaaaaaaaaaaaa
                           /
                          a  (displaced a strand)
    
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  3. Thirdly, the displaced a strand invades the other chromosome (this requires RecA)
    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaaccccccccccc aaaaaaaaaaaaaaa
                           /
                          /
    bbbbbbbbbbbbaaaaaaaaaa  bbbbbbbbbbbbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
    (the strand that has been replaced in chromosome 2 is degraded)
  4. Strand migration occurs
    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaacccccccccccbbbbbbbbbbb   aa
                                      \ /
                                       X
                                      / \
    bbbbbbbbbbbbaaaaaaaaaaaaaaaaaaaaaa   bb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    
  5. The junction may be resolved in one of two ways. One produces non-recombinant chromosomes with a heteroduplex region. The other produces recombinant chromosomes.

    (Type 1 - non-recombinant)

    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 1
    aaaaaaaaaaaacccccccccccbbbbbbbbbbbaaaaa
    
    
    bbbbbbbbbbbbaaaaaaaaaaaaaaaaaaaaaabbbbb
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    
    

    (Type 2 - recombinant)

    
    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbb
    Chromosome 1
    aaaaaaaaaaaacccccccccccbbbbbbbbbbbbbbbb
    
    
    bbbbbbbbbbbbaaaaaaaaaaaaaaaaaaaaaaaaaaa
    Chromosome 2
    bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbaaaaa
    
    

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