Synaptonemal complex analysis of a reciprocal translocation, rcp(20;24) (q17;q25), in a subfertile bull.

A reciprocal translocation was identified in a subfertile artificial insemination bull. Somatic chromosome investigation of G-banded metaphases demonstrated a 60,XY,rcp(20;24)(q17;q25) karyotype for the carrier. Synaptonemal complex analysis of the translocation by electron microscopy revealed an irregular pairing behavior of the chromosome axes involved, which resulted in a variety of configurations at pachytene. Not only was the expected quadrivalent configuration present, but also a trivalent plus univalent and two heteromorphic bivalents. Most common was an incompletely or completely paired quadrivalent configuration, which was non-homologously paired. XY association with the multivalent was seen only rarely. Histological analysis of testicular tissue showed meiotic arrest in some tubules. However, the semen picture was normal.