Select which examples are induced mutations.
A. Nitrous acid causes the deamination of cytosine to uracil.
B. lonizing radiation causes chromosomal fragmentation.
C. Errors in DNA replication cause the formation of point mutations.
D. Transposition causes the formation of deletions.
The Correct Answer and Explanation is:
Correct Answers: A and B.
Explanation:
Mutations are changes in the DNA sequence and can be classified into two broad categories: spontaneous mutations and induced mutations.
- Spontaneous mutations arise naturally without external influence, often due to errors in DNA replication or natural biochemical processes.
- Induced mutations, on the other hand, are caused by external agents known as mutagens, such as chemicals or radiation.
Now, let’s examine each option:
A. Nitrous acid causes the deamination of cytosine to uracil.
✅ Induced Mutation
Nitrous acid is a chemical mutagen that modifies DNA bases through deamination. Specifically, it converts cytosine to uracil, which then mispairs during replication, leading to point mutations. Since this is caused by a chemical agent external to the cell, it is classified as an induced mutation.
B. Ionizing radiation causes chromosomal fragmentation.
✅ Induced Mutation
Ionizing radiation, such as X-rays and gamma rays, is a physical mutagen. It can cause severe DNA damage, including double-strand breaks, which may result in chromosomal fragmentation and translocations. Because this damage results from an environmental factor, it is considered an induced mutation.
C. Errors in DNA replication cause the formation of point mutations.
❌ Spontaneous Mutation
This occurs naturally during the process of DNA replication. While cells have proofreading mechanisms, occasional mistakes can still occur, leading to base substitutions or insertions/deletions. Since this is not triggered by an external mutagen, it is a spontaneous mutation.
D. Transposition causes the formation of deletions.
❌ Spontaneous Mutation
Transposons, or “jumping genes,” can move around the genome, sometimes causing deletions or insertions. These are typically endogenous genetic elements that act without external triggers, making the resulting mutations spontaneous rather than induced.
Conclusion:
Only A (Nitrous acid) and B (Ionizing radiation) are induced mutations, as they are caused by external chemical or physical agents.
