Which of the following best describes a mutation that leads to a change in chromosome number?

A mutation that leads to a change in chromosome number is best described as aneuploidy. Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell, which can occur due to errors during cell division, such as nondisjunction. This condition results in the gain or loss of chromosomes, leading to genetic imbalances that can cause various developmental or health issues.

In contrast to aneuploidy, gene mutations typically involve changes in the nucleotide sequence of specific genes but do not affect the overall number of chromosomes. Point mutations are a specific type of gene mutation that involves a change in a single nucleotide. Chromosomal mutations, while they do involve changes to the structure of chromosomes (such as deletions, duplications, inversions, or translocations), do not specifically describe changes in the number of chromosomes. Therefore, the description requiring a change in chromosome count is accurately captured by the term aneuploidy.