Are the sex chromosomes (for humans X and Y ) expressed in all somatic cells? Or just those cells of organs that are related somehow to sexual phenotype (primary and secondary sexual characteristics)?

Question

Dylan Andrews · Accepted Answer

First thing first: There are genes on chromosomes and the genes are expressed. All genes on a chromosome are not expressed at one go.

The X chromosome has hundreds of genes on it and many of these are controlling characters related to organs other than the reproductive system.
For example, gene for colourblindness present on X, is responsible for maintenance of photoreceptors in healthy cone cells of retina.
Then there are genes on X chromosome which allow hepatic cells to produce clotting factors ; hence mutation in such X linked genes cause hemophilia.
So, It can not be said that genes on X chromosome are expressed only in cells associated with reproductive system; some of these genes are actually expressed in various somatic tissues of both sexes through entire life.
That is not entirely true for genes present on Y chromosome, because Y chromosome is present only in males: i.e. Y linked genes are absent in all female cells .
There is one AMELY gene on Y, that codes for extracellular enamel protein amelogenin which expresses during development of tooth enamel, a nonreproductive tissue but this is rather an exception.
Most of the Y-linked genes are expressed in organs of male reproductive system such as testes, prostate gland, etc.
Expression of SRY gene of Y chromosome initiates sex differentiation very early in embryonic life.
So, expression of genes on Y chromosome are restricted in male reproductive organs only, and some of these genes express for only a brief period of embryonic life.

Austin Alexander · Answer

undefined The sex chromosomes are present in all somatic cells but are only actively expressed in cells related to sexual phenotype.