Figure 1
From: How the vertebrates were made: selective pruning of a double-duplicated genome
A simplified schematic diagram of the 2R quadruplication and subsequent gene fates. A model gene encoding a two-domain protein is duplicated twice. Each of the top two copies loses one domain (function) during subfunctionalization; together they make up the function of the ancestral form. Another copy acquires a new domain and thus a new function (neofunctionalization). The last copy fails to serve a unique function and is lost. A similar process can cause loss and gain of expression regulatory elements.