Although the process of X inactivation in mammalian cells silences
the majority of genes on the inactivated X chromosome, some genes
escape this chromosome-wide silencing. Genes that escape X inactivation
present a unique opportunity to study the process of silencing
and the mechanisms that protect some genes from being turned off.
In this review, we will discuss evolutionary aspects of escape
from X inactivation, in relation to the divergence of the sex
chromosomes. Molecular characteristics, expression, and epigenetic
modifications of genes that escape will be presented, including
their developmental regulation and the implications of chromatin
domains along the X chromosome in modeling the escape process.