Fig 1.
Revising models for meiotic recombination.
Illustration depicts steps involved in the repair of meiotic DSBs. A DSB is suffered by one DNA duplex (chromatid) of a replicated parental chromosome (in this case, the “Mom” chromosome, green). 5′ termini on either side of the DSB are resected, and 3′ ssDNA tails assemble with the RecA homologs Rad51 (gray) and Dmc1 (pink) to create nucleoprotein filaments competent for strand invasion and exchange with a homologous duplex DNA. Available templates for repair include the sister (green) or either of two homologous chromatids (blue, “Dad” chromosome). The abbreviated pathway on the far left depicts a model based on the idea that Rad51 and Dmc1 assemble differentially on opposite 3′ termini corresponding to a single DSB. Data presented in Brown et al. [1] suggest instead that opposite 3′ termini corresponding to a DSB often load both Rad51 and Dmc1 (pathway at right). Strand invasion by one 3′ end followed by DNA synthesis can lead to a Holliday Junction structure. It remains to be determined whether opposite ends exhibit asymmetric behavior despite their equivalence in terms of Dmc1 and/or Rad51 loading—for example, whether one 3′ end is selectively released to initiate a search for a homologous duplex DNA (left branch) or alternatively whether both 3′ ends at a DSB exhibit equivalent homology search behavior (right branch).