Question

What is X - chromosome inactivation?

Answer 1

During early stages of development, one X chromosome in each somatic cell of a female embryo undergoes chemical modification and is inactivated. This is called X chromosome inactivation.

Explanation:

X chromosome inactivation renders one X chromosome ( in somatic cell ) transcriptionally silent. This is a random process, occurring in embryonic stage as parts of somatic tissue inactivate the maternal X chromosome and other parts inactivate the paternal X chromosome. However a handful of cells escape modification and actively express from both X chromosomes.
This does not normally occur in germ cells.