Figure 4.

Gene expression (+, −) from active (X_a) and inactive (X_i) X chromosomes and model for the chromosomal basis for genes escaping X inactivation. Six genes that escape inactivation map exclusively within a domain (denoted by the shaded oval) that is transcriptionally active on the inactive X chromosome. Genes mapping both distal and proximal to this domain are subject to inactivation, implying that they lie in different domains that are transcriptionally silent on the inactive X chromosome.