Synaptonemal complex

It is currently thought that the SC functions primarily as a scaffold to allow interacting chromatids to complete their crossover activities.

[1] The synaptonemal complex is a tripartite structure consisting of two parallel lateral regions and a central element.

This "tripartite structure" is seen during the pachytene stage of the first meiotic prophase, both in males and in females during gametogenesis.

[5] The sex chromosomes in male mammals show only "partial synapsis" as they usually form only a short SC in the XY pair.

[6] SYCP2 appears to confer cancer cell resistance to therapeutic DNA damaging agents by stimulating R-loop mediated double strand break repair.

For instance, in protozoan ciliates such as Tetrahymena thermophila and Paramecium tetraurelia genetic crossover does not appear to require synaptonemal complex formation.

Schematic of the synaptonemal complex at different stages during Prophase I
A Homologous chromosomes (light blue) align and synapse together via transverse filaments (black lines) and longitudinal filaments (dark blue). Recombination nodules (gray ellipsoids) on the central region may help in completing recombination. Chromatin (red loops) is attached to its sexual leg and toe, extending from both sister chromatids. B Top: Set of tomato SCs. Chromatin "sheaths" visible around each SC. Bottom: Two tomato SCs with the chromatin removed, allowing kinetochores ("ball-like" structures) at centromeres to be revealed.