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

Abstract

Summary. The

Aneuploid spermatocyte frequency in domestic sheep heterozygous for three Robertsonian translocations

“…However, it is probably premature, with the limited data available, to speculate on the significance of this correlation in sheep. In earlier meiotic studies, a significant excess of normal balanced secondary spermatocytes was found in single heterozygous rams (Chapman & Bruère, 1975;Long, 1978) but subsequent mating data demonstrated a balanced segregation pattern (Bruère & Ellis, 1979). Although it is possible that a process of cell selection during spermatogenesis results in the production of gametes in proportions which are significantly different from the expected ratio (1:1:2:2:1:1), it has previously been suggested by Ortavant (1958) and Roosen-Runge (1973) that the chromosomally abnormal cells in the ram and translocation-carrying rams (Bruère, 1974a; Chapman & Bruère, 1975) …”

“…The three triple heterozygous rams used were derived from the mating experiments reported previously (Bruère & Ellis, 1979). The karyotypes of the rams were determined by a whole blood leucocyte technique (Bruère & McLaren, 1967) and testicular material was obtained from testes after surgical castration under local anaesthesia.…”

“…From one such study there is little or no evidence to suggest that the centric fusions have any significant effect on the reproductive fitness of translocation-carrying sheep (Bruère, 1974a;Bruère & Chapman, 1974;Bruère & Ellis, 1979). Although significant levels of hypermodal secondary spermatocytes have been found in single heterozygous rams (t,, 5-63%;t2, 4-5%;t3, 9-2%, Chapman & Bruère, 1975;6-1% in t, only, Long, 1978), it is believed that these cells do not mature into aneuploid gametes.…”

Flow cytometric detection of unbalanced ram spermatozoa from heterozygous 1;20 translocation carriers

“…Bruere (1974Bruere ( , 1975. Bruere and Chapman (1974), Bruere and Ellis (1979), Long (1974Long ( , 1977Long ( , 1978b. and Stewart-Scott (1990. personal com munication) found no indications of reduced fertility among heterozygous carriers of the Robertsonian translocations Mas sey 1 through Massey 5, whereas Glahn-Luft and Wassmuth (1980) reported a reduction in twin and triplet pregnancies sired by heterozygous 1:20 translocation carriers.…”

Analysis of the 1/20 translocation in ram spermatozoa by flow cytometry

“…Structural rearrangements of chromosomes, including translocations can have adverse effects on fertility in humans (Daniel, 1988;Lange et al, 1990) and animals (Gustavsson, 1980;Eldridge, 1985;Daniel, 1988 (Bru!re, 1975;Long, 1977Long, , 1978Bru6re and Ellis, 1979). Long (1977) and Bru6re et al (1981) concluded that a selection mechanism in heterozygous translocationcarrying rams during spermatogenesis eliminates unbalanced secondary spermatocytes.…”