If the mutation is confined to a single-base substitution, then the only mutations possible are that CTA mutated to CGA or that GTG mutated to CGG. In both, there is a T : G transversion in the middle nucleotide of the codon. 2. A gene encodes a protein with the following amino acid sequence:
A mutation of a single nucleotide alters the amino acid sequence to:
What is the nature and location of the first mutation and the intragenic suppressor mutation?
The first mutation alters the reading frame, because all amino acids after Met are changed. Insertions and deletions affect the reading frame; so the original mutation consists of a single-nucleotide insertion or deletion in the second codon. The intragenic suppressor restores the reading frame; so the intragenic suppressor also is most likely a single-nucleotide insertion or deletion: if the first mutation is an insertion, the suppressor must be a deletion; if the first mutation is a deletion, then the suppressor must be an insertion. Notice that the protein produced by the suppressor still differs from the original protein at the second and third amino acids, but the suppressor's second amino acid is the same as that in the protein produced by the original mutation. Thus the suppressor mutation must have occurred in the third codon, because the suppressor does not alter the second amino acid.
3. The mutations produced by the following compounds are reversed by the substances shown. What conclusions can you make about the nature of the mutations originally produced by these compounds?
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