Potential advantages of unstable interactions for pairing of chromosomes in meiotic, somatic, and premeiotic cells.

Many different aspects of chromosome pairing, meiotic and/or somatic, can be explained conveniently if the interactions between homologous chromosomes are unstable. Initial pairing interactions should involve very unstable contacts. Such interactions could go a long way toward bringing each pair of homologous chromosomes into a joint domain, free of ectopic associations and random entanglements with other chromosomes, and in a topologically acceptable relationship to the domains of other chromosome pairs. More generally, colocalization into topologically acceptable domains could be a useful way of defining the existence of "order" at early stages in pairing; this definition requires that chromosomes have in some way recognized and interacted with one another but does not require that they necessarily be in close apposition and/or that they be aligned along their entire lengths. At later stages, interactions between pairing chromosomes could be unstable but still reversible, either intrinsically or due to an active cell-directed process. Transient homologous interactions could also contribute to maintaining colocalization between homologous chromosomes through DNA replication.