Coordinate variation in meiotic pachytene SC length and total crossover/chiasma frequency under conditions of constant DNA length

During meiosis, the number of crossovers, or their cytological correlates, chiasmata, vary in striking correlation to the length of prophase chromosome axes at the synaptonemal complex stage. Both parameters vary, and vary coordinately, among different individuals, strains or sexes, even when DNA length is effectively constant. Co-variation could be established either: (i) at or prior to recombination initiation via programmed double-strand breaks (DSBs); or (ii) at the time of crossover control, when a subset of DSBs is designated for future maturation as crossovers (chiasmata). Models in which chromosome axis length would determine recombination frequency are discussed.