A. BOUVET*, E.P. CRIBIU*, A. DE GIOVANNI**, and C.P. POPESCU*. *INRA-CRJ
Laboratoire de Cytogenetique, 78350, Jouy-en-Josas, France **Instituto di Zootecnia Generale, Facolta di Agraria, Universita degli Studi, Milano, Italia.
Analyses of surface-spread synaptonemal complexes of pachytene spermatocytes were performed on two subfertile bulls. One animal was carrying both the 1/29 and 9/23 robertsonian translocations whereas the other was the carrier of a 4/8 centric fusion. In all cells examined, the presence of a trivalent figure corresponding to the pairing of each translocated chromosome with its two normal homologues was easily detected since normal autosomal bivalents show a terminal centromeric region whereas in a trivalent the centromeres are located in a more central position. All spermatocytes from the first bull showed two trivalents figures whereas those from the second animal showed only one. In both cases, there was no association between the trivalents and the X-Y bivalent. This would explain why subfertile bulls carrying chromosome translocations have normal spermatogenesis, in contrast to human and mouse carriers of translocations which show impaired spermatogenesis due to the association between the abnormal complexes and the sex vesicle. The reduced fertility noted in this bulls could be explained by the production of chromosomally unbalanced gametes during meiosis, leading to embryo mortality after fertilisation.
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