Mutations and Their Effects
Types of Mutations
Mutation Classes
Mutations can be point mutations, insertions, deletions, duplications, inversions, or translocations. Their effects range from neutral to severe, depending on where they occur and how they alter gene function.
Coding Sequence Consequences
A silent mutation changes a codon without changing the amino acid. A missense mutation changes one amino acid. A nonsense mutation creates a premature stop codon. Insertions or deletions that are not multiples of three can cause a frameshift.
Frameshift Severity
Frameshifts often have large effects because they alter every codon downstream of the mutation.
Which mutation is most likely to create a premature stop codon?
A nonsense mutation directly creates a stop codon.
Correct answer: Nonsense
What is a frameshift mutation?
This alters codon grouping downstream of the mutation.
Correct answer: An insertion or deletion not in multiples of three that changes the reading frame.
Which mutation changes one amino acid to another?
Missense mutations alter the encoded amino acid.
Correct answer: Missense
Mutation Sources
Mutations arise from replication errors, chemical mutagens, radiation, and mobile genetic elements. Cells and environments both contribute to mutation rates.
Why can a mutation be neutral even if it changes DNA?
Many DNA changes have no observable phenotype.
Correct answer: Because it may not change the protein, occur in a noncritical region, or affect expression.