Comparative FISH mapping of bovid X chromosomes reveals homologies and divergences between the subfamilies bovinae and caprinae.

Comparative FISH mapping of river buffalo (Bubalus bubalis, BBU), sheep (Ovis aries, OAR), and cattle (Bos taurus, BTA) X chromosomes revealed homologies and divergences between the X chromosomes in the subfamilies Bovinae and Caprinae. Twenty-four and 17 loci were assigned for the first time to BBU X and OAR X, respectively, noticeably extending the physical map in these two species. Seventeen loci (four of which for the first time) were also FISH mapped to BTA X and used for comparative mapping studies on the three species, which show three morphologically different X chromosomes: an acrocentric (BBU X), an acrocentric with distinct short arms (OAR X), and a submetacentric (BTA X). The same order of loci were found on BTA X and BBU X, suggesting that a centromere transposition, with loss (cattle) or acquisition (river buffalo) of constitutive heterochromatin, differentiated the X chromosomes of these two bovids. Comparison of bovine (cattle and river buffalo) and caprine (sheep) X chromosomes revealed at least five common chromosome segments, suggesting that multiple transpositions, with retention or loss of constitutive heterochromatin, had occurred during their karyotypic evolution.