Let's evaluate each statement about substitution mutations:
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Always harmful – False: Not all substitution mutations are harmful; some may have no effect (silent mutations), while others may have beneficial effects.
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Only harmful if a resulting amino acid of the codon is changed – True: This is generally accurate. If the substitution changes the amino acid, it may affect protein function, but if it does not (as in silent mutations), it may not be harmful.
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Never harmful – False: Substitution mutations can indeed be harmful, especially if they lead to a change in protein function.
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Sometimes silent mutations and not expressed – True: Some substitution mutations are silent, meaning they do not change the amino acid sequence of the protein and thus may not have any effect.
So, the correct evaluations are:
- Always harmful: False
- Only harmful if a resulting amino acid of the codon is changed: True
- Never harmful: False
- Sometimes silent mutations and not expressed: True