What defines a chromosomal mutation?

A chromosomal mutation is characterized by alterations in the structure or number of chromosomes within an organism's cells. This can include changes such as duplications, deletions, inversions, or translocations of chromosome segments, as well as aneuploidy, which refers to an abnormal number of chromosomes. Such mutations can have significant effects on an organism's development, physiology, and overall health, as they can disrupt the normal balance of genes and lead to various genetic disorders.

In this context, option A accurately captures the essence of chromosomal mutations, emphasizing that the defining feature is the alteration of chromosomes themselves. Chromosomal mutations can lead to conditions such as Down syndrome (trisomy 21) or Turner syndrome (monosomy X), illustrating their profound impact on human biology and health.