Why is the outcome of a base-pair substitution mutation variable? List and describe the possible outcomes of a base-pair substitution mutation in your answer

Question

What will be an ideal response?

Answer 1

Answer: The outcome of a base-pair substitution mutation is variable because multiple codons can code for the same amino acid. For example, ACC, ACG, and ACU all encode for alanine (codon examples do not necessarily have to be correct, but should convey the concept). Often the third position of the codon can change without changing the amino acid. In addition, some amino acids have similar properties (e.g., leucine and isoleucine), thus changing particular amino acids may not have much of a phenotypic affect. There are three possible outcomes of a point mutation. Silent mutations can have slightly modified protein structures or unmodified ones, as long as the nucleotide change does not result in any change of the phenotype. Missense mutations are more restricted in that a nucleotide change results in a particular amino acid (codon) change. Although a missense mutation will change the amino acid sequence, this again may or may not change the structure of the protein and the phenotype. A nonsense mutation is the most specific of all where the nucleotide sequence now contains an inserted non-native stop site. The premature halt of protein synthesis will result in a shortened protein structure and will likely change the phenotype of the organism.