X-inactivation (also called lyonization)'s a process by which one of the two copies of the X chromosome present in female mammals's inactivated. The inactive X chromosome's silenced by packaging into transcriptionally inactive heterochromatin. X-inactivation occurs so that the female, with two X chromosomes, doesn't have twice as many X chromosome gene products as the male, which only possess a single copy of the X chromosome (see dosage compensation). The choice of which X chromosome will be i… (More on Lyonization)