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. 2017 Feb 17:2–43.e19. doi: 10.1016/B978-0-323-35775-3.00001-1

E-Figure 1-25.

E-Figure 1-25

Types of Base-Pair Substitutions in Gene Mutations.

1, Silent mutations. Base-pair substitutions in silent mutations change the messenger RNA (mRNA) codons (GGU to GGG in the example); however, the mutated codons (GGG) code for the same amino acid as the original mRNA codons, so the synthesis of the polypeptide is unaffected. 2, Missense mutations. Base-pair substitutions in missense mutations change the mRNA codons (UGG to UCG in the example); the mutated codons (UCG) code for a different amino acid than the original mRNA codons, so the synthesis of the polypeptide is altered. 3, Nonsense mutations. Base-pair substitutions in nonsense mutations change the mRNA codons (UGG to UGA in the example); the mutated codons (UGA) are a “stop” code, prematurely halting polypeptide chain synthesis. tRNA, Transfer RNA.

(Courtesy Dr. M.A. Miller, College of Veterinary Medicine, Purdue University; and Dr. J.F. Zachary, College of Veterinary Medicine, University of Illinois.)