What term describes an abnormal number of a particular chromosome?

The term "aneuploid" describes an abnormal number of a particular chromosome in a cell. This condition occurs when the number of chromosomes is not an exact multiple of the haploid number, which leads to a gain or loss of one or more chromosomes. For instance, in humans, a typical diploid cell has 46 chromosomes, and if there is an aneuploid condition such as trisomy 21, there are three copies of chromosome 21 instead of the usual two.

In contrast to aneuploidy, "polyploid" refers to a cell having more than two complete sets of chromosomes, which is common in some plants but not typically in animals. "Diploid" indicates the normal state for most human cells, containing two sets of chromosomes (one from each parent), while "haploid" refers to cells that contain only one set of chromosomes, as seen in gametes (sperm and egg cells). Understanding these definitions is important for grasping how chromosomal abnormalities can lead to various genetic conditions.