Which of the following is not a chromosomal mutation?

A single point mutation refers to a change that occurs at a specific position within a gene, affecting only one nucleotide base pair. This type of mutation typically involves the substitution, addition, or deletion of a single nucleotide. It is classified as a small-scale mutation, affecting only a limited region of DNA, rather than a larger chromosomal alteration.

In contrast, chromosomal mutations encompass changes that involve larger segments of DNA and can include various types of structural changes in chromosomes, such as duplications, inversions, or translocations. Additionally, alterations to the chromosomal number, known as aneuploidy, represent another category of chromosomal mutations that involve gains or losses of entire chromosomes. Deletions of chromosome segments also fall under this category, as they involve the removal of larger portions of the chromosomal structure.

Thus, the distinction lies in the scale and impact of the mutation. Single point mutations are localized, whereas chromosomal mutations typically involve broader changes that can have significant effects on an organism's genome and phenotype.