Synaptonemal complex analysis in a human male carrier of a 4;6 translocation: heterosynapsis without previous homosynapsis.

Silver-stained synaptonemal complexes in surface-spread pachytene nuclei from a man, heterozygous for a reciprocal translocation, were analysed by electron microscopy. Contrary to the classically expected cross-shaped configuration, extensive non-homologous pairings were observed with asymmetrical association in the lateral elements of the non-homologous arms of the quadrivalents. A possible role of the heterosynapsis in reproductive failure is discussed.