A MOLECULAR CYTOGENETIC ANALYSIS OF X-CHROMOSOME REPATTERNING IN THE BOVIDAE - TRANSPOSITIONS, INVERSIONS, AND PHYLOGENETIC INFERENCE

Chromosomal homologies among the X chromosomes of species representati ve of eight bovid subfamilies and most of the recognized tribes were e stablished using a combination of FISH and conventional G- and C-bandi ng. Our analyses allowed for the delimitation of three X chromosome ty pes represented, respectively, by cattle (Bovinae, tribe Bovini), the tragelaphines (Bovinae, tribe Tragelaphini), and a large assemblage co mprising all the remaining subfamilies and their tribes (the Cephaloph inae, Hippotraginae, Alcelaphinae, Antilopinae, Aepycerotinae, Peleina e, and Caprinae). The use of the bacterial artificial chromosome probe BAC 101 (which maps to Xp12 in cattle) and an Xp painting probe compr ising sequences specific for the short arm of cattle Xp (Xp24-->p12) a llowed us to orient this region, which has moved as a conserved euchro matic block during the evolution of the bovid X chromosome. We show th at the differences between the three chromosomal types are attributabl e to a transposition, two inversions, and heterochromatic additions/de letions. A paucity of comparative mapping data precludes the assignmen t of the sequences contained in cattle Xp to either the presumed conse rved (XCR) or the recently added (XAR) region of the eutherian X chrom osome, and the reasons for the retention of these sequences as an evol utionarily conserved unit in the intrachromosomal restructuring of the bovid X across lineages remain enigmatic.