Dosage compensation is the process by which organisms equalize the expression of genes between members of different biological sexes. It refers to the equalization of most X-linked gene products between males, which have one X chromosome and a single dose of X-linked genes, and females, which have two X chromosomes and two doses of X-linked genes. Dosage compensation mechanisms balance the levels of X-linked gene products between the sexes. In females, genes on one X chromosome are silenced. In Drosophila melanogaster, transcription of the single male X chromosome is upregulated by twofold in a process orchestrated by the dosage compensation complex. The modification of chromatin structure is a general principle of dosage compensation systems in various organisms.