Heterosynapsis in a heterozygous fertile boar carrier of a 3;7 translocation.

Silver-stained synaptonemal complexes (SCs) in surface-spread pachytene nuclei from a boar, heterozygous for a reciprocal translocation, were analysed by electron microscopy. In such heterozygotes, cross-shaped quadrivalent configurations are expected to form in order to maximize homologous pairing. Contrary to the classical, expected cross-shaped configuration, heterosynapsis was often observed, with asymmetrical association in the lateral elements of the non-homologous partners of the quadrivalents. This heterosynapsis is assumed to be a mechanism preventing spermatocyte loss, but inducing a secondary segregational type of impairment of fertility due to foetal wastage leading to reduced prolificacy.