X-inactivation is the process by which one of the two X chromosomes present in females is inactivated
- This ensures that females do not produce twice as many X-linked gene proteins as males (who possess one X chromosome)
The silenced X chromosome is packaged as transcriptionally inactive heterochromatin, forming a structure called a Barr body
- Once an X chromosome is inactivated, it will remain permanently inactive in the cell (and all cells derived from it)
X-inactivation occurs randomly in mammals, meaning both X chromosomes may be active in different cells
- This allows for a heterozygous phenotype to occur in the female as a whole
X-Inactivation and the Formation of a Barr Body
