Question

A mutation called a (n) ________ often results in a frameshift that garbles the genetic message. a. deletion b. insertion c. base-pair substitution d. a or b

Short answer

d. a or b

Step-by-step solution

Understand the Options

There are four options provided: a deletion, an insertion, a base-pair substitution, or either a deletion or an insertion. We need to determine which type of mutation causes a frameshift.

Define Frameshift Mutation

A frameshift mutation is a genetic mutation caused by insertions or deletions of nucleotides in a DNA sequence that changes the reading frame. This alters the downstream amino acid sequence.

Analyze the Effects of Deletion

A deletion removes nucleotides from a DNA sequence. If the number of deleted nucleotides is not divisible by three, it shifts the reading frame, causing a frameshift mutation.

Analyze the Effects of Insertion

An insertion adds extra nucleotides into a DNA sequence. Similar to deletions, if the number of inserted nucleotides is not in multiples of three, it results in a frameshift mutation.

Analyze Base-Pair Substitution

Base-pair substitution replaces one nucleotide with another. This does not cause a shift in the reading frame because it does not add or remove nucleotides.

Conclusion

Both deletions and insertions can result in frameshift mutations that alter the genetic message when they change the reading frame.

Key concepts

Deletion

A deletion mutation occurs when a segment of DNA loses one or more nucleotide bases. The impact of such a mutation on the genetic information largely depends on how many bases are removed.
A deletion can lead to severe consequences if the number of nucleotides removed is not a multiple of three. DNA sequences are read in groups of three, known as codons, each of which codes for a specific amino acid during protein synthesis.

• **Frameshift Mutation**: When nucleotide bases are deleted in numbers not divisible by three, the reading frame of the DNA sequence is disrupted. This shifts the entire sequence that follows, potentially garbling the genetic message and leading to nonfunctional proteins.
• **Impact on Protein Function**: As the reading frame changes, different codons might now code for unintended amino acids. Also, premature stop codons often emerge, truncating the protein prematurely. This can result in a significant loss of protein function or total loss of function.

Insertion

Insertion mutations involve the addition of one or more nucleotide bases into the DNA sequence. Similar to deletions, the consequence of insertions depends on the number of bases added.

• **Frameshift Mutation**: Insertions that do not occur in multiples of three nucleotides cause the reading frame to shift. This frameshift affects all downstream codons, which can dramatically alter the structure and function of the resulting protein.
• **Genetic Message Alteration**: The addition of extra nucleotides changes the way the sequence is read, potentially inserting incorrect amino acids into the protein sequence. This often leads to dysfunctional proteins, or even to a completely nonfunctional protein.

Moreover, frameshift mutations caused by insertions are often detrimental because they not only disrupt the primary structure of proteins but may also lead to new stop codons that prematurely end translation.

Base-Pair Substitution

Base-pair substitution is a type of mutation where one nucleotide base in the DNA is replaced by another. Unlike deletions and insertions, this does not change the overall length of the DNA sequence, hence does not result in a frameshift.

• **Silent Mutation**: Sometimes, a base-pair substitution causes no changes in the protein sequence. This occurs if the new codon still codes for the same amino acid.
• **Missense Mutation**: This happens when the substitution results in a different amino acid being inserted into the growing peptide chain. The impact can vary; it may have little effect or it could significant impact the protein's function depending on the role of the altered amino acid.
• **Nonsense Mutation**: If the substitution creates a stop codon, the resulting mutation is a nonsense mutation. This type of mutation typically leads to nonfunctional proteins due to premature termination of protein synthesis.

Overall, while base-pair substitutions might not cause frameshift mutations, they could still significantly affect protein functionality depending on where and what type of change occurs.