Reconstruction of the ancestral primate XIST locus and comparison of multispecies conserved regions. Horizontal lines represent the XIST locus in human and the reconstructed primate ancestor. Human exons (dark blue); ancestral primate DNA corresponding to those exons (gray). Each XIST-specific repeat (A, B, Bh, C, D, E, F) is color-coded and shown with approximate size and location. (Dark gray boxes) Approximate locations of conserved noncoding sequences (CNS). See Figure 6 for more details about each CNS. (Open triangles) Human and ancestrally reconstructed primate-specific insertions. (Triangles without a label) Insertion of nonrepetitive sequence.