Figure 4. Variety of fluorescent proteins produced by in vitro selection—how molecular evolution can be used to solve a complex practical problem. Here DNA shuffling in a constructed synthetic green fluorescent protein (GFP) gene was used to increase the whole-cell fluorescence signal of GFP in Chinese hamster ovary cells. The GFP mutant in B shows the improvement in signal over the wild-type version in A. Source: Crameri A., Whitehorn E.A., Tate E., and Stemmer W.P.C. 1996. Improved green fluorescent protein by molecular evolution using DNA shuffling. Nat. Biotechnol. 14: 315–319 (p. 318, Fig. 5A,B). http://www.nature.com