In contrast to the sex chromosomes, the autosomal genome is shared by both sexes. However, although the DNA sequence, gene structure, and frequency of polymorphisms on the autosomes do not differ between males and females, the regulatory genome is sexually dimorphic23-26. That is, sex-specific differences in gene regulation (rather than gene content) probably underlie most phenotypic sexual dimorphism, including sex-specific effects on human diseases. Indeed, at the mRNA level, sexually dimorphic gene expression has been observed in a wide range of organisms, including worms27, flies28,29, fish30, rodents 25,31, and primates23. Although genes with sex-biased expression are enriched on the sex chromosomes, thousands of sex-biased genes are also found on the autosomes.
