Figure 1.

Sites of mitotic and meiotic recombination in C. elegans. The gonads of C. elegans are a syncitium of nuclei, which is organized spatiotemporally. At the distal most region known as “distal tip” (purple) germ-line nuclei divide mitotically, before entering meiosis I (indicated by dotted line). During mitosis, HR typically occurs in response to stalled replication forks, whereas in meiosis, it is a normal consequence of programmed DSBs occurring in the first stages of prophase I. In the transition zone (leptotene/zygotene), DSBs are formed and chromosomes pair, and in C. elegans, this stage is visually distinguishable as the nuclei become C-shaped. In pachytene, chromosomes synapse, and DSBs are repaired to form at least one crossover between homologs. In diplotene through diakinesis, the synaptonemal complex is disassembled, and the paired chromosomes condense to form bivalents that will be packaged into each oocyte (for an extensive review of chromosome dynamics during prophase I in worms, see Woglar and Jantsch 2014).