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. Author manuscript; available in PMC: 2018 Apr 30.
Published in final edited form as: Adv Exp Med Biol. 2017;966:103–148. doi: 10.1007/5584_2017_93

Figure 16.

Figure 16

Alternative mechanisms for genetic code expansion. A. Strand specialization. Daughters produced by gene duplication evolve first by breaking the genetic linkage between bi-directional coding sequences, producing specialized genes that express from only one of the two strands. B. Adaptive radiation. The code is expanded by producing pairs of bi-directional genes, both strands of which have specialized functions. (A) and (B) should lead to different patterns in the degree of middle codon-base pairing. (Adapted with permission from the Society for Molecular Biology and Evolution. Chandrasekaran, SN et. al. (2013) Mol. Biol. Evol. 30: 1588–1604.)