Synaptonemal complex analysis by electron microscopy showed a trivalent formed by pairing of chromosome 17(7) with chromosome pair 7 in two zygotene cells. In 89 pachytene cells (75.4%) the chromosome 17(7) occurred as a univalent with the axis being unpaired, in the shape of a ring (60.6%), a rod (38.2%) or self-paired (1 cell). Thirty-four (38.2%) of the univalents were paired or associated with the sex bivalent. Twenty-five (21.2%) of the 118 pachytene cells analysed demonstrated different types of trivalent pairing: the 17(7) chromosome paired with chromosome pair 7 in 24 cells and with pair 17 in one cell. Moreover, in 4 cells, chromosome 17(7) was paired with both pair 7 and pair 17, forming a pentavalent. Trivalent association with XY was observed in 4 cells. Nineteen bivalents plus a univalent (8 cells), and eighteen bivalents plus a trivalent (11 cells), were found during conventional meiotic investigation of diakinesis-metaphase I. Though the boar demonstrated a normal testicular histology, a qualitatively deviant semen picture was evident.
