Biological systems exhibit complex patterns at length scales ranging from the molecular to the organismic. Along chromosomes, events often occur stochastically at different positions in different nuclei but nonetheless tend to be relatively evenly spaced. Examples include replication origin firings, formation of chromatin loops along chromosome axes and, during meiosis, localization of crossover recombination sites ("crossover interference"). We present evidence in the fungus Sordaria macrospora that crossover interference is part of a broader pattern that includes synaptonemal complex (SC) nucleation. This pattern comprises relatively evenly spaced SC nucleation sites, among which a subset are crossover sites that show a classical interference distribution. This pattern ensures that SC forms regularly along the entire length of the chromosome as required for the maintenance of homolog pairing while concomitantly having crossover interactions locally embedded within the SC structure as required for both DNA recombination and structural events of chiasma formation. This pattern can be explained by a threshold-based designation and spreading interference process. This model can be generalized to give diverse types of related and/or partially overlapping patterns, in two or more dimensions, for any type of object.spatial patterning | synapsis initiation site | recombination/synapsis | crossover designation M eiosis is the specialized cellular cycle that yields haploid gametes for sexual reproduction. A central feature of the meiotic program is recombination (1, 2). DNA/DNA recombination interactions, initiated by programmed double-strand breaks (DSBs), mediate the recognition and juxtaposition (pairing) of homologous chromosomes. A minority subset of these interactions matures into reciprocal crossover recombination products (COs); the remaining majority matures primarily into interhomolog non-crossover products (NCOs). COs promote genetic diversity but also are required for the segregation of homologous chromosomes (homologs) via their role in creating chiasmata (3).A nearly universal feature of meiosis is that COs occur along a particular chromosome at different positions in different meiotic nuclei. Nonetheless, along any given chromosome, COs tend to be evenly spaced. This pattern results from the reduced possibility that a second cross-over will occur if a crossover has occurred nearby. The existence of such a pattern was identified more than a century ago as the genetic phenomenon of CO interference (4, 5). In this phenomenon, occurrence of a CO in one genetic interval is accompanied by a reduced probability that another CO will occur along the same chromosome in a nearby interval. This effect implies the existence of communication along chromosomes, with an event at one position triggering occurrence of an "interference signal" that spreads outward, inhibiting occurrence of subsequent events nearby.A second central feature of the meiotic program is the synaptonemal complex (SC). This prominent structure link...