A molecular cytogenetic analysis of X chromosome repatterning in the Bovidae: transpositions, inversions, and phylogenetic inference

Chromosomal homologies among the X chromosomes of species representative of eight bovid subfamilies and most of the recognized tribes were established using a combination of FISH and conventional G- and C-banding. Our analyses allowed for the delimitation of three X chromosome types represented, respectively, by cattle (Bovinae, tribe Bovini), the tragelaphines (Bovinae, tribe Tragelaphini), and a large assemblage comprising all the remaining subfamilies and their tribes (the Cephalophinae, Hippotraginae, Alcelaphinae, Antilopinae, Aepycerotinae, Peleinae, and Caprinae). The use of the bacterial artificial chromosome probe BAC 101 (which maps to Xp12 in cattle) and an Xp painting probe comprising sequences specific for the short arm of cattle Xp (Xp24-->p12) allowed us to orient this region, which has moved as a conserved euchromatic block during the evolution of the bovid X chromosome. We show that the differences between the three chromosomal types are attributable to a transposition, two inversions, and heterochromatic additions/deletions. A paucity of comparative mapping data precludes the assignment of the sequences contained in cattle Xp to either the presumed conserved (XCR) or the recently added (XAR) region of the eutherian X chromosome, and the reasons for the retention of these sequences as an evolutionarily conserved unit in the intrachromosomal restructuring of the bovid X across lineages remain enigmatic.