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Reliable, easy-to-read patient information on common medical conditions — written in plain language, free of jargon, and grounded in current evidence. Browse the most frequent diagnoses, understand what they mean for everyday life, and learn which steps and questions help you have a focused conversation with your doctor.

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Synapsis

Introduction

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.

References

  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.