Final answer:
The inactive X chromosome in females has methylation of DNA and hypo-acetylation of histones as an epigenetic mark, which causes the nucleosomes to pack loosely together and inactivate one of the X chromosomes.
Step-by-step explanation:
The inactive X chromosome in females has methylation of DNA and hypo-acetylation of histones as an epigenetic mark. This causes the nucleosomes to pack loosely together, inactivating one of the X chromosomes.
The tighter packing of nucleosomes prevents gene expression, which is why one of the X chromosomes becomes inactive.