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Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis.[1] Synapsis takes place during prophase I. When homologous chromosomes synapse, they come closer together until they are connected by a protein complex called the synaptonemal complex, which contains central and lateral elements.[2] While autosomes undergo synapsis during meiosis sex chromosomes usually remain unpaired.[3]

When the non-sister chromatids intertwine, segments of chromatids with the same sequence break apart at and are exchanged in a process known as genetic recombination or "crossing-over". Recombination exchanges genetic material between homologous chromosomes and increases the genetic variability of the offspring. This exchange produces a chiasma, a region that is shaped like an X, where the two chromosomes are physically joined.

The opposite of synapsis is disjunction.


  1. McKee B (2004). "Homologous pairing and chromosome dynamics in meiosis and mitosis". Biochim Biophys Acta. 1677 (1–3): 165–80. PMID 15020057.
  2. Revenkova E, Jessberger R (2006). "Shaping meiotic prophase chromosomes: cohesins and synaptonemal complex proteins" (PDF). Chromosoma. 115 (3): 235–40. PMID 16518630.
  3. Page J, de la Fuente R, Gómez R, Calvente A, Viera A, Parra M, Santos J, Berríos S, Fernández-Donoso R, Suja J, Rufas J (2006). "Sex chromosomes, synapsis, and cohesins: a complex affair" (PDF). Chromosoma. 115 (3): 250–9. PMID 16544151.