Bovine pseudoautosomal boundary (PAB). Corresponding Y- and X-derived sequences were aligned using ClustalW, revealing (1) a region of near perfect homology (red) corresponding to the PAR, (2) a region of reduced homology (orange) resulting from the displacement of the PAB by attrition, and (3) nonhomologous gonosome-specific segments (green). (Black arrow) Present-day bovine PAB, (white arrow) ancestral PAB. (Lowercase letters) Repetitive sequences, (uppercase letters) unique sequences. (Red) Monomer domain of the Bov-tA repeat overlapping the ancestral PAB, (blue) tRNA-like domains differentiating the Bov-tA1 repeat of the X and the Bov-tA2 repeat of the Y.
