The Chromosomes of Sheep X Goat Hybrids

Abstract

Hybrid foetuses carried by female goats after mating with male sheep usually die within 2 months of conception (see Alexander, Williams, and Bailey 1967). Since the chromosome number of 54 in the sheep (Makino 1943; Borland 1964; see Plate 1, Fig. 2, for illustration) differs from the 60 in the goat (Makino 1943; Basrur and Coubrough 1964), it is possible that death of these hybrids is due to the development of cell lines with abnormal numbers of chromosomes resulting from mitotic non-disjunction. Berry (1938) could find no evidence of chromosomal nondisjunction in sheep X goat hybrids. However, his display of chromosomes was considerably less clear than those produced by modern methods, and this led to the study by Buttle and Hancock (1966). They reported variations of 53-58 chromosomes per cell in cultures of a minced hybrid embryo, and concluded that it was not possible, on the available evidence, to reject the possibility that death was due to chromosomal non-disjunction; only 5 of 14 cells contained 57 chromosomes. Subsequently, Hancock and Jacobs (1966), using uncultured cells, found fewer departures from the expected number of 57 chromosomes in the hybrid embryos than in the previous study, and fewer departures (10 in 135 cells) in the hybrids, than in sheep and goat embryos (6 in 30 and 6 in 23 cells, respectively).