The Frequency of Aneuploidy in the Secondary Spermatocytes of Normal and Robertsonian Translocation-Carrying Rams

Cytogenetics and reproduction of sheep with multiple centric fusions (Robertsonian translocations)

“…However high levels of aneuploidy are also consistent with high frequencies of zygotic loss Cattanach & Moseley, 1973). It is therefore reasonable to propose that, since all three centric fusions of domestic sheep produce consistent levels of aneuploid secondary spermatocyte frequency in the heterozygous state (Chapman & Bruère, 1975) The breeding system and animal husbandry from which the present results were derived were the same as reported previously (Bruère, 1974a(Bruère, , 1975 Bruère (1974aBruère ( , 1975 (2) and (3) was used as a measure for conception rate and embryonic survival. The difference between (4) and (5) was used as a measure of reproductive rate and can also be a useful indicator of inbreeding depression (Lax & Brown, 1968).…”

“…In no instance was there a serious fall in fertility as has been recorded in the ¥l of the tobacco mouse domestic mouse and the Apennine mouse laboratory mouse (Capanna et al, 1976). Pending the analysis of the triple hétérozygotes (t1t2t3) for levels of aneuploid secondary spermatocyte frequency, it would appear that although this may be shown to be higher than in single hétéro¬ zygotes (Chapman & Bruère, 1975) it does not lead to production of aneuploid zygotes. It should, however, be emphasized, that as in mice (White et al, 1978) the levels of aneuploidy in individual hétérozygotes need not necessarily correlate with those of the combined hétéro¬ zygotes, although in many examples an increase has been described Cattanach & Moseley, 1973).…”

“…This has been demonstrated from accumulated breeding data and from normal segregation ratios which result from the products of crossing sheep that have centric fusions in various mating categories (Bruère, 1974a;Bruère, 1975;Long, 1978b). It is believed that the normal reproductive performance and the balanced segre¬ gation ratios reported in these breeding data were produced because only balanced gametes took part in fertilization although aneuploid secondary spermatocytes were recorded at significant levels in all heterozygous rams (t" 5-63%; t2, 4-5%; t3, 9-2% (Chapman & Bruère, 1975); 6-1% in t" only (Long, 1978a)). …”

Meiosis and spermatogenesis in bulls heterozygous for a presumptive 1/29 Robertsonian translocation

“…However, extensive studies of Robertsonian translocation in sheep raises some doubts as to the general applicability of this hypothesis (Bruère, 1976). No detectable deleterious effect on the fertility of carrier male or female sheep has been shown in over 1000 matings, despite the fact that raised levels of non-disjunction have been found in carrier rams (Chapman & Bruère, 1975;Bruère, 1976). Furthermore, in a study of 102 13-18 day-old embryos, offspring of carrier rams and normal Blackface ewes, no unbalanced chromosome complements of any type were detected (Long, 1976).…”

“…No detectable deleterious effect on the fertility of carrier male or female sheep has been shown in over 1000 matings, despite the fact that raised levels of non-disjunction have been found in carrier rams (Chapman & Bruère, 1975;Bruère, 1976). Furthermore, in a study of 102 13-18 day-old embryos, offspring of carrier rams and normal Blackface ewes, no unbalanced chromosome complements of any type were detected (Long, 1976). Chapman & Bruère (1975 and Long (1976) have proposed that there was a prezygotic selection of spermatozoa, but it is possible that the gametic products of nondisjunction events formed unbalanced embryos and that these died in the first 12 days of life and were amongst the relatively large proportion (25%) which Long (1976) could not karyotype.…”