At evolgen, a blogger sums up recent research on sexually antagonistic genes. Several papers look across species, from human, mouse, and fruit fly, at the effect of X-linked copies of genes -- genes from the X-chromosome that are duplicated and appear on autosomes and are expressed in a biased fashion in male- and female-specific tissues. In one paper, Brian Oliver of the NIH looked across different Drosophila species to conclude that natural selection drives male-biased genes off the X chromosome independently of the effects of X inactivation during spermatogenesis.