Final answer:
In human cells, dosage compensation is achieved by the inactivation of one of the two X chromosomes in females, a process called X inactivation.
Step-by-step explanation:
Dosage compensation in human cells is achieved by inactivating one X chromosome of females. This process, known as X inactivation, occurs early in development when female mammalian embryos have only a few thousand cells. One X chromosome is randomly chosen to inactivate by condensing into a Barr body, ensuring that females compensate for their double genetic dose of X chromosome. This inactivation is passed on to all daughter cells, maintaining dosage compensation throughout development.