Investment into reproduction comes with a cost to survival. For males this occurs because they risk injury when in combat with other males and elevated predation when displaying for females, and for both sexes because limited resources are allocated away from somatic maintenance. The degree an individual can afford to invest into reproduction should therefore depend on the amount of resources he or she has access to, and traits exposed to sexual or sex-specific selection should hence evolve condition dependent expression. Condition dependence of male sexual traits is the cornerstone of the good genes theory for why females choose their mates. The idea is that females through mating with males with exaggerated display traits provide good genes for their offspring, as the expression of these traits reveal the genetic quality of males (provided genetic quality influences condition). While the theory hinges on that expression of male display traits depend on males’ genetic quality, the theory has almost exclusively been tested by manipulating condition through the environment, and the few studies that have varied condition through genetic quality have provided inconsistent results. The large amount of genes which show sex-biased expression provide a fantastic opportunity to test the theory of condition dependence of sexual traits on a large scale. Clever manipulations of condition through environmental and genetic quality, coupled to studies of gene expression, promise to provide unprecedented insight into how condition dependence is distributed over phenotypes and the sexes. In this project we are undertaking this task, varying condition through genetic quality by comparing gene expression of inbred and outbred and locally adapted to naïve individuals. We are comparing these results to when condition is varied through the environment. In addition we are also plan to investigate how age influences sex differences in gene expression.