Figure 1: Features of the X chromosome sequence.

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a, X chromosome ideogram according to Francke⁶⁵. b, Evolutionary domains of the X chromosome: the X-added region (XAR), the X-conserved region (XCR; dotted region in proximal Xp does not appear to be part of the XCR), the pseudoautosomal region PAR1, and evolutionary strata S5–S1. c, Sequence scale in intervals of 1 Mb. Note that correlation between cytogenetic band positions and physical distance is imprecise, owing to varying levels of condensation of different Giemsa bands. d, (G + C) content of 100-kb sequence windows. e, Number of genes in 1-Mb sequence windows (pseudogenes not included). f–k, Fractional coverage of 100-kb sequence windows by interspersed repeats: L1 repeats (f), L1M subfamilies of L1 repeats (g), L1P subfamilies of L1 repeats (h), Alu repeats (i), L2 repeats (j), MIR repeats (k). Vertical grey lines in d–k represent gaps in the euchromatic sequence of the chromosome. Grey bar centred at approximately 60 Mb shows the position of the centromere. l, A selection of landmark genes on the chromosome. OPN refers to the three opsin genes in the reference sequence, which are organized as follows: cen-OPN1LW-OPN1MW-OPN1MW-tel. m, Genes that escape from X-chromosome inactivation as previously identified⁴⁸. n, Cancer-testis antigen genes, belonging to the MAGE (light green), GAGE (dark green), SSX (magenta), SPANX (orange) or other (grey) CT gene families. For the genes in l–n, arrows indicate the direction of transcription.