Figure 1.

Regulation of gene expression on sex chromosomes relative to autosomes in males (M) and females (F) of mammals and Drosophila (XX female:XY male), and birds (ZW female:ZZ male). Basal autosome-equivalent expression level is in light blue; upregulated regions are represented in dark blue and inactivated regions in white. Genes on the two Z chromosomes of the male bird are presumed to have equal expression to the autosomes, but the single Z of female birds is only partially dosage compensated (orange shading represents a mixture of genes compensated to various degrees). The heterochromatic and largely inactive or specialized Y and W chromosomes are represented in yellow.