We want to track the evolution of altered gene expression in males via fine-scale adjustment of dosage compensation effects in Drosophila. By carrying out male-limited X-chromosome evolution, X-linked genes are released from constraints arising from selection in females and are free to specialize for male fitness. Based on previous results we expect that this will result in alteration of dosage compensation effects. Sex-specific fitness is highly context-dependent (43), so this setup will allow us to investigate how dosage compensation effects can be modulated in response to shifting sex-specific selection pressures. Altered patterns of gene expression in Male-limited X-chromosome evolution in Drosophila will be detected by RNA-seq to see how the upregulation and down-regulation of X-linked male and female-biased genes respectively affect male fitness. Male limited expression of the X-chromosome can be enforced through the use of females with a connected (or double) X. These DX females also carry a Y, and so when a normal XY male is crossed to a DX female then sons with a paternally inherited X and maternally inherited Y are produced, as are new DX daughters which have a maternally inherited DX and a paternally inherited Y (double-Y embryos are inviable, and triple-X females do not survive to adulthood). Three experimental evolution populations and three control populations have been set up, with a population size of 640 individuals each. To avoid clonal interference on the X, a “recombination box” has been used. Genomic data will be collected every 10 generations has been collected and in total, we have RNAseq data from 7 time-series points.