3.8.1 Understanding Gene Mutations and Effects

What is a gene mutation?

• A change in the sequence of amino acids in a protein

• A change in the sequence of bases in DNA

• A change in the number of chromosomes

• A change in the structure of a cell

Answer explanation

A gene mutation specifically refers to a change in the sequence of bases in DNA. This alteration can affect how proteins are made, but the mutation itself is defined at the DNA level, not at the protein or cellular level.

Which of the following is NOT a type of gene mutation?

• Addition

• Deletion

• Translocation

• Translation

Answer explanation

Translation is a process of protein synthesis, not a type of gene mutation. The other options, addition, deletion, and translocation, are all recognized types of mutations that alter the DNA sequence.

What is the effect of a substitution mutation on the encoded polypeptide?

• It always results in a frame shift

• It may result in a different amino acid

• It always results in a stop codon

• It duplicates the entire gene

Answer explanation

A substitution mutation may change one nucleotide, potentially altering one amino acid in the polypeptide. This is why the correct answer is that it may result in a different amino acid, rather than causing a frame shift or a stop codon.

What is a frame shift mutation?

• A mutation that changes one base pair

• A mutation that changes the reading frame of the genetic code

• A mutation that duplicates a segment of DNA

• A mutation that inverts a segment of DNA

Answer explanation

A frame shift mutation occurs when nucleotides are added or deleted, altering the reading frame of the genetic code. This can lead to significant changes in the resulting protein, making the correct choice "A mutation that changes the reading frame of the genetic code."

Which of the following can increase the rate of gene mutations?

• Mutagenic agents

• High temperatures

• Low pH levels

• High humidity

Answer explanation

Mutagenic agents are substances that can cause changes in DNA, leading to increased rates of gene mutations. High temperatures and low pH can also affect DNA stability, but mutagenic agents are specifically known for inducing mutations.

What is the degenerate nature of the genetic code?

• Each amino acid is coded by only one codon

• Each codon codes for multiple amino acids

• Multiple codons can code for the same amino acid

• Codons are not specific to any amino acid

Answer explanation

The genetic code is degenerate because multiple codons can code for the same amino acid, allowing for redundancy. This means that while there are 64 possible codons, only 20 amino acids are used, leading to multiple codons for some amino acids.

Which type of mutation involves the reversal of a segment of DNA?

• Inversion

• Duplication

• Translocation

• Substitution

Answer explanation

An inversion mutation occurs when a segment of DNA is reversed within the chromosome. This contrasts with duplication, translocation, and substitution, which involve different alterations to the DNA structure.

What is the result of a deletion mutation?

• An extra base is added to the DNA sequence

• A base is removed from the DNA sequence

• A base is replaced with another base

• A segment of DNA is inverted

Answer explanation

A deletion mutation specifically involves the removal of a base from the DNA sequence, which can lead to changes in the protein produced. Therefore, the correct answer is that a base is removed from the DNA sequence.

How can a single base substitution mutation be silent?

• It occurs in a non-coding region of DNA

• It results in a stop codon

• It does not change the amino acid due to the degenerate code

• It causes a frame shift

Answer explanation

A single base substitution can be silent if it does not change the amino acid due to the degenerate code, where multiple codons can code for the same amino acid, thus not affecting protein function.

Which mutation type can result in a longer polypeptide chain?

• Substitution

• Deletion

• Addition

• Inversion

Answer explanation

An addition mutation introduces extra nucleotides into the DNA sequence, which can lead to the incorporation of additional amino acids in the resulting polypeptide chain, making it longer. Other mutations typically do not increase length.