It is known that humans and Drosophila “buffer” their double dose of sexual chromosomes (females have two X chromosomes whereas males have only one). Basically one of the two X chromosomes becomes inactive during development.
This week there is a paper published in the Journal of Biology that shows that birds behave differently “sexualchromosomicallywise”. In the case of birds, males are the ones with the double dose. But in this case both chromosomes are active, in fact males express sex-linked genes at higher levels than females.
It’s speculated that this might be involved in the generation of sexual dimorfism.