Aneuploidy

Aneuploidy (from Greek an = not, eu = correct, normal and -ploid = -fold): Numerical chromosome aberration, deviation from the normal number of chromosomes.

Aneuploidies are caused by distribution disorders during cell division ( mitosis or meiosis ). In contrast, other terms with the part of speech ~ploidy such as triploidy, tetraploidy and polyploidy refer only to the number of whole chromosome sets. Thus, in triploidy, all homologous chromosomes are present in triplicate. In the absence or excess number of individual chromosomes, on the other hand, the word ~somy is used (cf. trisomy in Down syndrome).