True or false: X chromosome inactivation equalizes the gene dosage between mammalian males and females.

True or false: X chromosome inactivation equalizes the gene dosage between mammalian males and females.

• A. True
• B. False
• C. Not exactly
• D. It is not related to dosage

Answer: (A)

X chromosome inactivation is a mechanism of dosage compensation in mammals. In males, there is one X chromosome, so X-linked genes are expressed from that single copy. In females, although there are two X chromosomes, one is largely silenced in each cell, so most X-linked genes are expressed from only one active X. This silencing is initiated by XIST RNA and maintained through cell divisions, producing a mosaic pattern because different cells inactivate different X chromosomes. Across tissues, this balances the overall expression of X-linked genes between sexes, though a small number of genes can escape inactivation and fire from both X chromosomes, creating some exceptions.

X chromosome inactivation is a mechanism of dosage compensation in mammals. In males, there is one X chromosome, so X-linked genes are expressed from that single copy. In females, although there are two X chromosomes, one is largely silenced in each cell, so most X-linked genes are expressed from only one active X. This silencing is initiated by XIST RNA and maintained through cell divisions, producing a mosaic pattern because different cells inactivate different X chromosomes. Across tissues, this balances the overall expression of X-linked genes between sexes, though a small number of genes can escape inactivation and fire from both X chromosomes, creating some exceptions.