Multiple Choice
A section of DNA has this base sequence: AGCGTTACCGT. A mutation in this DNA strand results in this base
sequence: AGGCGTTACCGT. What type of mutation does this change represent?
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15. Gene Expression
Mutations
1:55 minutesProblem 6
Textbook Question
A geneticist found that a particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involved
a. Deletion of one nucleotide
b. Alteration of the start codon
c. Insertion of one nucleotide
d. Substitution of one nucleotide
Verified step by step guidance1
Understand the problem: The question is asking about a mutation that does not affect the polypeptide encoded by a gene. This means the mutation is 'silent' and does not change the amino acid sequence of the resulting protein.
Review the genetic code: The genetic code is redundant, meaning multiple codons can code for the same amino acid. A substitution of one nucleotide in a codon might still result in the same amino acid being incorporated into the polypeptide. This is known as a 'silent mutation.'
Analyze the options: A deletion or insertion of one nucleotide (options a and c) would cause a frameshift mutation, altering the reading frame of the gene and likely changing the entire amino acid sequence downstream of the mutation. This would have a significant effect on the polypeptide.
Consider the start codon (option b): Alteration of the start codon would prevent the ribosome from initiating translation properly, which would have a drastic effect on the polypeptide, likely preventing its synthesis altogether.
Focus on substitution (option d): A substitution of one nucleotide could result in a silent mutation if the new codon still codes for the same amino acid. This is the most likely explanation for a mutation that has no effect on the polypeptide.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Silent Mutation
A silent mutation is a change in the DNA sequence that does not alter the amino acid sequence of the resulting polypeptide. This can occur due to the redundancy in the genetic code, where multiple codons can code for the same amino acid. Understanding silent mutations is crucial for interpreting how certain genetic changes can be phenotypically neutral.
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Types of Mutations
Mutations can be classified into several types, including substitutions, insertions, and deletions. A substitution involves replacing one nucleotide with another, while insertions and deletions add or remove nucleotides, respectively. The impact of these mutations on protein function varies, with some potentially leading to significant changes, while others may have no effect.
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Codon and Amino Acid Relationship
Codons are sequences of three nucleotides in mRNA that correspond to specific amino acids during protein synthesis. The relationship between codons and amino acids is fundamental to understanding how genetic information is translated into functional proteins. Changes in codons can lead to different outcomes, such as silent mutations, missense mutations, or nonsense mutations, depending on the nature of the change.
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