X chromosome inactivation in X autosome translocation carrier cows.

The pattern of X chromosome inactivation in X autosome translocation carries in a herd of Limousin-Jersey crossbred cattle was studied using the reverse banding technique consisting of 5-bromodeoxyuridine incorporation and acridine orange staining and autoradiography on cultures of solid tissues and blood samples exposed to tritiated thymidine. The late-replicating X chromosome was noted to be the normal X in strikingly high proportions of cells in cultures of different tissues from all translocation carriers. It is suggested that the predominance of cells in which the normal X is inactivated may be the result of a post-inactivation selection process. Such a selection process during the prenatal life favouring cells in which the genes of the normal X chromosome remain unexpressed in translocation carrier females may be the mechanism that helps these conceptuses escape the adverse effects of functional aneuploidy. Based on the observation that the translocation carriers of this line of cattle are exclusively females and that there is a higher than expected rate of pregnancy loss, it is also postulated that the altered X chromosome may be lethal to all male conceptuses and to some of their female counterparts.

A cytogenetic study of subfertility in the domestic cat (Felis catus).

The chromosomes of cat embryos derived from three subfertile queens were studied 4 weeks postcoitum. The incidence of spontaneous chromosome anomalies was 15% and type of abnormality observed was autosomal mosaicism. The significance of this finding and the developmental fate of the chromosomally aberrant embryos is discussed. The absence of polyploidy and (nonmosaic) autosomal trisomy, which are the most common observations in previous studies on mammalian embryos, suggests that the difference between the present observations and previous studies may be related to the difference in gestational stage studied, or to the difference in ovulatory patterns between domestic cats and other mammals. Polyploidy through ageing of the gametes is less likely in the cat than in spontaneous ovulators since ovulation in cats is induced only after coitus. It is speculated that chromosome analysis of earlier stages of embryonic development may reveal more severe forms of karyotype alteration.