What refers to the presence of an abnormal number of chromosomes in a cell?

Aneuploidy refers to a condition in which there is an abnormal number of chromosomes within a cell, typically characterized by the presence of either one extra chromosome or one fewer than the standard diploid number for that organism. For example, in humans, the normal chromosome count is 46; thus, having 47 chromosomes (as seen in Down syndrome) reflects an aneuploid condition.

This term specifically describes the deviation from the typical chromosomal complement, which can have significant implications for an organism's development and function, often leading to various genetic disorders or syndromes. In contrast, duplication involves the replication of a chromosome segment, translocation refers to the rearrangement of chromosome segments between non-homologous chromosomes, and inversion occurs when a segment of a chromosome is reversed end to end. These terms describe different types of chromosome mutations but do not encompass the broader concept of having an abnormal number of chromosomes.