The evolution of gene expression and the transcriptome-phenotype relationship

► Gene expression evolution is an important and overlooked mechanism of phenotype evolution. ► Nascent models of transcriptome evolution have been developed to study the selective and neutral forces shaping gene expression evolution. ► These models are not yet as robust as similar models of coding sequence evolution, and will benefit from the development of null models of transcriptome evolution as well as the incorporation of different types of expression evolution.