What describes a substitution mutation?
Multiple choice question.
two DNA bases are deleted or inserted
one DNA base is inserted
one DNA base is replaced with another
one DNA base is deleted
The Correct Answer and Explanation is :
Correct Answer:
One DNA base is replaced with another
Explanation:
A substitution mutation occurs when a single DNA nucleotide is replaced by another. This type of mutation is often categorized as a point mutation because it affects only a single nucleotide within the DNA sequence. Substitution mutations can result in different consequences depending on the nature of the substitution and the region of the genome it occurs in.
Substitution mutations can be further classified into two main types:
- Transition Mutations:
In this type, a purine base (adenine or guanine) is replaced by another purine, or a pyrimidine base (cytosine or thymine) is replaced by another pyrimidine. For example:
- Adenine (A) replaced by Guanine (G)
- Cytosine (C) replaced by Thymine (T)
- Transversion Mutations:
This involves the replacement of a purine by a pyrimidine or vice versa. For example:
- Adenine (A) replaced by Cytosine (C)
- Thymine (T) replaced by Guanine (G)
Effects of Substitution Mutations:
- Silent Mutation:
The substituted base results in a codon that codes for the same amino acid, having no effect on the protein’s function. - Missense Mutation:
The change in the base results in a different amino acid, which may alter protein structure and function. For example, sickle cell anemia results from a missense substitution in the hemoglobin gene. - Nonsense Mutation:
The substitution creates a stop codon, leading to premature termination of protein synthesis, which may produce a nonfunctional protein.
Substitution mutations are distinct from insertions and deletions, which involve adding or removing nucleotides and often cause frameshifts. These differences highlight how substitution mutations specifically replace one base while preserving the sequence’s length.