What does aneuploidy refer to in genetics?

Aneuploidy specifically refers to a condition where the number of chromosomes in a cell is not the typical diploid number for that organism. This can occur when there is an addition or loss of one or more chromosomes, resulting in an abnormal number of chromosomes, which may lead to genetic disorders or developmental issues.

For example, in humans, a common form of aneuploidy is Down syndrome, which arises from an extra copy of chromosome 21, resulting in three copies instead of the usual two. This highlights how aneuploidy directly pertains to variations in chromosome number rather than structural alterations of chromosomes, protein variations, or differences in DNA sequences. Such precise definitions are crucial for understanding genetic mutations and their implications in various biological contexts.