What does aneuploidy mean?
Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell — either too many or too few — as opposed to changes affecting entire sets of chromosomes. In humans, who normally have 46 chromosomes arranged in 23 pairs, aneuploidy usually arises when chromosomes fail to separate properly during cell division, producing cells with an extra chromosome (a trisomy) or a missing one (a monosomy). Most cases are lethal early in development, which is why aneuploidy is a leading cause of miscarriage; survivable examples include Down syndrome, caused by an extra copy of chromosome 21, and Klinefelter syndrome. The term belongs to the vocabulary of genetics, reproductive medicine, and oncology, where aneuploidy in tumour cells signals genomic instability. Its adjective form, aneuploid, describes the affected cell or organism. For anyone following prenatal screening results or reading about cancer biology, aneuploidy is an essential concept to understand.
nounThe condition of having an abnormal number of chromosomes in a cell, involving either extra or missing chromosomes rather than whole extra sets.
- An abnormal number of chromosomes in a cell, involving gains or losses of individual chromosomes rather than whole chromosome sets.
"Prenatal screening can detect fetal aneuploidy such as trisomy 21."
"Most human embryos with aneuploidy fail to implant or miscarry early in pregnancy."
"The cancer cells showed widespread aneuploidy, a hallmark of genomic instability."
The plural follows standard English formation; it appears mainly in research writing discussing multiple distinct chromosomal abnormalities.
"Several different aneuploidies were identified across the sampled embryos."
Down syndrome results from just one extra copy of chromosome 21 — that single surplus chromosome makes it the most common human aneuploidy.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of aneuploidy
Aneuploidy derives from Greek roots: the negative prefix 'an-' ('not'), 'eu-' ('good' or 'true'), and '-ploidy' from Greek 'ploos' meaning 'fold', via the German 'Euploidie' coined by geneticist Günter Winkler in the early twentieth century. It literally means a condition in which chromosome number is not a true multiple of the basic set. It shares these roots with related terms such as euploidy, polyploidy, haploid, and diploid, all part of the cytogenetic vocabulary built on the same 'fold' root.
Related word forms
How aneuploidy is actually used
Strictly technical term used in genetics, medicine, and cell biology; rarely encountered in everyday speech. It is typically discussed in clinical contexts such as prenatal testing and cancer research.
Easily confused with aneuploidy
Polyploidy involves one or more complete extra sets of chromosomes, whereas aneuploidy involves only individual extra or missing chromosomes.
Nondisjunction is the cellular error that causes aneuploidy, not the resulting chromosomal condition itself.