Meiotic recombination is homologous recombination occurring during meiosis. It can exchange segments between homologous chromosomes through crossing over, while noncrossover recombination repairs or changes local sequence without reciprocal exchange of the chromosome arms. These outcomes connect the repair of DNA with reshuffling of inherited alleles.
In budding yeast, a decisive experiment purified DNA ends carrying a covalently attached protein from mutants that accumulated meiotic DNA double-strand breaks. The attached protein was identified as Spo11, strongly implicating it in catalysing the initiating cleavage rather than merely responding after accidental damage.[ref]
Meiosis-specific DNA double-strand breaks are catalyzed by Spo11, a member of a widely conserved protein family by Scott Keeney and others. 1997, abstract: protein-linked breaks, purification and Spo11 identification
For an illustrative two-marker example, suppose the replicated homologues carry AB and ab. A single reciprocal exchange between the genetic markers, involving one chromatid from each homologue, can leave four chromatids carrying AB, Ab, aB and ab. Two are recombinant for those markers and two retain the parental combinations. More generally, the relation between observed marker combinations and physical exchanges depends on the positions and number of exchanges.
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