Rec'd recombination

The mammalian recombination machinery is determined to act, according to results from Huiling Xu, Michael McKay (Peter MacCallum Cancer Centre, Melbourne, Australia), and colleagues. If meiotic homologues are not properly positioned, the machinery sets up on sister chromatids instead.

Proper homologue positioning required Rec8, McKay's group showed. In yeast, Rec8 is known to be essential for recombination and for the formation of the synaptonemal complex (SC), which first links the homologues. In mice lacking Rec8, however, the SC was still laid down—but between sister chromatids rather than homologues. Rec8 thus somehow prevents SC formation between sisters normally.

Chromosome pairing appeared normal in the mutant germ cells, but the pairs might not be presented correctly. “Early on in premeiotic prophase,” says McKay, “Rec8 may have a structural role in creating...