1. A gene contains the sequence CGGCATACGGTACT that results in the amino acid sequence arg-ile-arg-tyr. A mutation in this gene removes the first G in the strand. What is true of this mutation's effect on the phenotype?
Answer: B
This mutation will affect the phenotype because all the amino acids past this point will be different from the original protein.
The removal of the first G in the gene's sequence will lead to a frameshift mutation, altering the reading frame for the entire sequence downstream. As a result, the sequence of amino acids produced after the mutation will diverge significantly from the original sequence, impacting the protein's structure and function.
A) It will not affect the phenotype because the protein will be identical to the original protein.
This option is incorrect as the mutation introduces a frameshift, which alters the entire sequence of amino acids following the mutation site. Therefore, the protein produced will not be identical to the original protein.
B) It will affect the phenotype because all the amino acids past this point will be different from the original protein.
This is the correct option. The mutation causes a frameshift, changing the reading frame and resulting in a completely different amino acid sequence from the point of mutation onwards, which likely alters the protein's functionality and affects the phenotype.
C) It will not affect the phenotype because only the first amino acid is different from the original protein.
This choice is incorrect. While the first amino acid will indeed be different, the frameshift caused by the mutation will lead to all subsequent amino acids being altered as well. Hence, the overall impact on the protein and phenotype is significant.
D) It will affect the phenotype because although most of the protein will be identical, the first amino acid will be different.
This option is misleading. While it acknowledges that there will be a change, it incorrectly suggests that most of the protein remains identical. In reality, the frameshift mutation alters the reading frame, resulting in a completely different amino acid sequence beyond the first amino acid.
Conclusion
The correct answer, B, highlights the significant impact of the frameshift mutation on the entire amino acid sequence downstream of the mutation point. All other options fail to recognize the extent of the changes caused by the frameshift, underestimating the mutation's effect on the protein's structure and, consequently, on the phenotype.