Possible outcomes for gene retention after whole-genome duplication. An ancestral network of interacting proteins is shown. Following a whole-genome duplication event, all of the proteins together with their interactions are duplicated. Over time, depending upon the evolutionary forces that are operating on the genome, different interactions are retained, gained or lost. Under the dosage-compensation model (bottom left), all interactions are retained. Under the subfunctionalization model (bottom center), redundant interactions become nonredundant (blue). When this is combined with the neofunctionalization model (bottom right), new interactions are also gained (red). In this figure, all of the duplicated copies have been retained as functional genes, but that is not the most likely outcome with increasing evolutionary time.