Heterochromatin, one of two chromatin types derived from a chromosome acts as to ensure repression of gene transcription or silencing. There are two types of heterochromatin; constitutive heterochromatin and facultative heterochromatin.
X-chromosome inactivation is an example of hetrochromatin silencing genes where the heterochromatin takes the form of a structure known as a Barr body. X chromosome inactivation is due to Xist transcription being activated in later development of the embryo whereas Tsix transcription is inactivated in the X chromosome being silenced. Tsix transcription remains activated in the active form of the X chromosome whereas Xist is silenced.