Meiosis,II: A modified affinity model in mice

In male mice, observations on MI clustering of nonhomologues in 4-armed tri-bivalent groups considered together with estimates of chiasma frequency in the same clusters, has suggested a modification of theWallce affinity hypothesis. According to the proposed model three classes of nonhomologous linkage would be generated by such a tribivalent figure; two of the three would vary inversely—and the third directly—with ordinary intrabivalent linkage frequencies. The model has the advantage of not requiring the existence of mesocentric chromosomes and furthermore appears attractive because of possible analogy with segregation patterns resulting from non-homologous association ofDrosophila andNeurospora. A possible disadvantage of the model is its dependence on chromatid interference.