A single base substitution is LEAST likely to be deleterious (dangerous) when the change results in _____.

• A. Replacement of a codon specifying a hydrophilic amino acid with a codon that specifies a hydrophobic amino acid.
• B. Replacement of a codon which codes for an amino acid with a stop codon.
• C. The change of a codon specifying a specific amino acid important for the active site of the protein.
• D. Replacement of a codon specifying an amino acid with a redundant codon specifying the same amino acid.

Answer: (D)

Verified step by step guidance

1. Understand the concept of a single base substitution, which is a type of point mutation where one nucleotide base is replaced by another in the DNA sequence.
2. Recognize that the genetic code is degenerate, meaning that multiple codons can code for the same amino acid. This is known as redundancy in the genetic code.
3. Consider the impact of different types of single base substitutions: a substitution that results in a synonymous codon (one that codes for the same amino acid) is less likely to affect the protein's function.
4. Evaluate the options given: a substitution that changes a codon to a synonymous codon (redundant codon) is least likely to be deleterious because it does not alter the amino acid sequence of the protein.
5. Conclude that the least deleterious effect occurs when the substitution results in a codon that specifies the same amino acid, maintaining the protein's structure and function.