A 4/21 tandem fusion in cattle

A tandem fusion involving chromosome 4 and chromosome 21 of the bovine karyotype, is described in a newborn Holstein-Friesian heifer which was also a blood chimera exhibiting female cells of normal bovine karyotype and male cells with a 59, XY + tan (4:21). The rearranged chromosome was a dicentric and the longest acrocentric in the male cells. Apart from the features characteristic of the freemartin condition, no other phenotypic abnormalities were detected in the heifer calf. Since the heifer and other calves of the herd were not eartagged at birth, 20 newborn bull calves of the same age in the herd were analyzed in an attempt to identify the male born co-twin to the heifer. However, this effort proved unsuccessful, probably because the co-twin had died in utero or was erroneously included among the calves sent to the slaughter house.

Meiotic peculiarities in hybrid buffalo

The two varieties of the Water buffalo (Bubalis bubalis var. bubalis and Bubalis bubalis var. carabao) have 2n = 50 and 2n = 48 karyotypes, respectively. The F1 hybrids are thought to exhibit a karyotype of 2n = 49 and are known to be fertile. Meiosis was studied in 10 hybrid water buffalo bulls. Karyotypes of the bulls were prepared from leukocyte cultures and testicular biopsy samples in a routine manner and examined. Phenotypically the bulls showed characteristics of the hybrid buffalo. Five of the bulls carried 2n = 50 and 5 had 2n = 49. Multivalent chromosomes were found in diakinesis (metaphase I) cells of bulls with 2n = 49 karyotypes. Synapses were found in bulls of both karyotypes.

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.

Isochromosome Y in an infertile heifer

The chromosome makeup of a 3-year-old crossbred heifer was examined in an attempt to explore the cytogenetic causes of her infertility. The heifer proved to be a mosaic carrying predominantly XY cells and with approximately 30% of cells lacking a normal Y. The minor population included cells carrying a dicentric isochromosome Y and a small proportion of XO cells. Histological features of the gonads and reproductive system suggest that the presence of cells resulting from isochromosome formation and the consequent loss of the Y chromosome segment required for testicular induction may have been causally related to the embryonic state of the gonads and malformation of the duct system noted in this heifer.