Sterility in hybrid cattle

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Abstract
The distribution of constitutive heterochromatin and nucleolus organizer regions (NORs) in somatic as well as in meiotic chromosomes of Bos taurus, Bos banteng, Bison bison, and their hybrids are analyzed. C-bands are present in the centromeric regions of every autosome. The X chromosome does not show a distinct C-band in the centromeric region, whereas the Y chromosome contains an appreciable amount of C-band material. In somatic metaphases, NORs are present on the telomeric ends of five pairs of autosomes. During pachytene, five autosomal bivalents contain NORs on their terminal ends. Meiotic preparations made from sterile bulls did not contain stages beyond the degenerating pachytene, which after C-banding, more frequently showed clustering of heterochromatin than did the pachytene stage in normal bulls.