Figure 1. Establishment of homologue pairing. (a) Homologue pairing could, in principle, take place uniformly along the chromosome, with any region equally likely to initiate pairing. (b) Experimental evidence suggests instead that homologues initially pair at discrete sites (Fung et al., 1998). This could either reflect the repeated sequence nature of the initiation sites or could be the result of special pairing proteins that bind to these sites. (c) Initial contact could occur either by random walk diffusive motion, or by a more directed active motility. (d) Following initial contact at one site, nearby sites can pair more easily, leading to a gradual pairing of the entire chromosome.

Figure 2. Role of nuclear organization in homologue pairing. (a) Constrained diffusion can enhance interactions between loci whose confinement regions overlap. (b) Alternatively, constrained diffusion can prevent interactions between loci with nonoverlapping confinement regions. (c) The Rabl configuration prealigns homologous chromosomes so that homologous loci occupy the same position along the Rabl axis. (d) Nuclear envelope associations cause homologous loci to occupy similar radial positions in the nucleus.