Zygotene (from greek "paired threads"[1]) is the second stage of prophase I during meiosis, the specialized cell division that reduces the chromosome number by half to produce haploid gametes.
Synapsis began during the previous leptotene stage, with the homologous chromosomes starting to pair together and associate lengthwise, facilitated by the synaptonemal complex protein structure.
It zips the homologs together along their entire length, with the lateral elements of the complex associated with each chromosome and the central region holding them together.
[5] As synapsis completes, proteinaceous recombination nodules begin to appear along the synaptonemal complex between the homologous chromosomes.
These represent sites of genetic crossover events, where exchange of chromosomal segments occurs between the non-sister chromatids.