Synaptonemal complex analysis of hybrid and purebred water buffaloes (Bubalus bubalis)

The morphology of the synaptonemal complex (SC) in river (2n = 50) and swamp (2n = 48) water buffaloes and their hybrids, was studied by electron microscopic analysis. In 2n = 49 hybrids, F2 and backcrosses the formation and pairing behaviour of a trivalent at zygotene-pachytene confirmed that river and swamp buffaloes differ by a centromere-to-telomere (C-T) tandem fusion. While 29% of spermatocytes from a purebred river buffalo and 16% from a purebred swamp buffalo had pairing abnormalities, a significantly higher frequency of abnormalities (48-72%) was recorded in F1, F2, and backcrosses with 2n = 48, 49 or 50. Highest abnormality frequencies occurred in 2n = 49 bulls. Abnormal pairing configurations often resulted from interactions between unpaired chromosome axes or segments. Zygotene-pachytene meiotic progress appeared delayed in hybrid bulls, and the frequency of SC abnormalities decreased from XY type I substage to type V substage. The variation in SC abnormality data from hybrids was consistent with the levels of sperm abnormality previously reported.