Fig. 4. Progression of SC formation (SC; red). (A) Synaptic forks at the points of synaptic progress are associated with TNs (green foci, arrows). The inflections (i) suggest a structural connection between the two homologs at the site of the TN. At later prophase, the chromosomes are completely synapsed and the SCs can have 10 or more TNs each (SC #1). The centromeres (cen; red) are frequently the last to pair. (B) Immunogold-defined positions of TNs at zygotene. The synaptic fork has two TNs labelled with 5-nm gold particles. The lateral elements (LEs) are labelled with 10-nm gold particles. (C) A mature pachytene SC with lateral elements and medially located TNs (10-nm gold). The width of the SC is approximately 250 nm.