Synaptonemal Complex

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The synaptonemal complex (SC) is a large proteinaceous structure that holds together homologous chromosomes during Meiosis, providing the structural framework for meiotic recombination and crossover formation. It is an evoluntionarily-conserved protein assembly which forms between homolgous chromosomes. The synaptonemal complex begins to form during the zygotene phase of Prophase I in the first division in Meiosis and is complete in the pachytene phase. Acting like a 'zipper' it holds the homologous chromosomes together, aligning them perfectly. After complete synapsis, crossing over occurs and in the diplotene phase, where the chiasma is visible, the synaptonemal complex 'unzips' and disappears [1].

The SC was discovered in 1956 and studies by electron microscopy have shown that in all sexually reproducing organisms in which it is found the complex adopts the same tripartite structure. It is made up of two lateral elements of approximately 50nm each that coat the chromosome axes, and in almost all organisms a central element of 20-40nm wdie. The elements continue along the entire chromosome axis[2][3].


  1. Hartl DL and Jones EW (2009) Genetics: Analysis of Genes and Genomes, Seventh Edition, USA, Jones and Bartlett Publishers
  2. Syrjänen JL, Pellegrini L, Davies OR. A molecular model for the role of SYCP3 in meiotic chromosome organisation. eLife 2014, 3, e02963
  3. Owen R. Davies, Joseph D. Maman, Luca Pellegrini (2012) Open Biol 2 120099; DOI: 10.1098/rsob.120099. Published 18 July 2012

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