Final answer:
Inversion is not classified as a gene mutation since it does not change the sequence of nucleotides within a gene but rather involves the reversal of a DNA segment within the chromosome.
Step-by-step explanation:
The question is asking which of the listed options is NOT a type of gene mutation. The options given were substitution, insertion, deletion, and inversion. A gene mutation is a permanent alteration in the DNA sequence that makes up a gene. We have:
- Substitution: One base pair is replaced by another.
- Insertion: One or more base pairs are inserted into the DNA sequence.
- Deletion: One or more base pairs are removed from the DNA sequence.
- Inversion: A section of DNA is reversed within the chromosome.
Among these, substitution, insertion, and deletion all directly alter the gene's coding sequence by adding, removing, or replacing nucleotides. However, an inversion does not change the actual genetic code but instead changes the orientation of a DNA segment within the chromosome. Therefore, while an inversion is a type of chromosomal mutation, it is not specifically a gene mutation, which would alter the sequence of nucleotides within a gene.
Answer: d. inversion is NOT a gene mutation.