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.