Females have twice as many copies of the X-chromosomes as males. Do females produce twice as much of the proteins encoded on the X-chromosome? No, because one of the X-chromosomes is condensed into an inactive form in all somatic cells.
The inactive X-chromosome in female somatic cells, visualized as a densely staining body within the nucleus and attached to the nuclear envelope, is known as a "Barr body." Females contain patches of cells in which one or the other X-chromosome has been inactivated, leading to a mosaic pattern of X-chromosome gene expression in different parts of the female body.