Illustration of the different evolutionary fates of (functional) duplicate genes. Each gene/protein is represented in different colors: red, ancestral, 'A'; green, duplicate copy A1; and blue, duplicate copy A2. Different shapes of proteins (circle, square, and triangle) indicate different functions. Three different subcellular localizations (nucleus, cytoplasm, and cytoplasmic membrane) are indicated in a schematic cell. We note that only the major possible scenarios are illustrated here.