Ploidy refers to the number of chromosomes found in a cell and is subdivided into two categories: euploidy and aneuploidy. Euploidy is one complete chromosome set or exact multiples of that set. Aneuploidy includes gain or loss of chromosomes that is less than a complete set. The optimum chromosome complement is fixed for each organism and can be described in terms of euploidy and aneuploidy, though the later is most often associated with variation or errors in the normal chromosome number.

Euploidy can refer to a broad range of chromosome findings. Haploidy, designated as the N number, is one complete chromosome set in which each chromosome is unique. Diploidy (2N) is two complete chromosome sets (pairs of chromosomes), triploidy (3N) is three sets, tetraploidy (4N) is four sets, and so on. Any cell with three or more chromosome sets is said to be polyploid. In humans, cells are...