FIGURE 1.

Different scales of variable escape from XCI. (a) Genes variably escape from XCI such that the gene escapes XCI in some individuals and is subject to XCI in other individuals (Cotton et al., 2013). (b) Tissue‐specific variable escape from XCI is observed for some genes, which have a consistent XCI status in some tissues, but the opposite XCI status in other tissues (Tukiainen et al., 2017). (c) Heterogeneous escape from XCI occurs at the level of single cells, with some cells escaping from XCI while other cells are subject to XCI. TIMP1 shows a random pattern while for MSL3 one allele is subject to XCI while another allele escapes from XCI (discussed in Tukiainen et al., 2017)