What does aneuploid mean?
Aneuploid describes a cell or organism whose chromosome number is abnormal — not an exact multiple of the species' haploid set. Rather than gaining or losing whole sets, an aneuploid cell has too many or too few individual chromosomes: a human cell might carry three copies of chromosome 21 instead of two, or lack a single copy of another. The term pervades modern biology and medicine. Cancer biologists note that most tumours are aneuploid, with chromosomal chaos driving malignant growth, while fertility specialists use preimplantation genetic testing to identify aneuploid embryos, since such embryos often fail to implant or miscarry. Well-known conditions such as Down syndrome (trisomy 21) result from aneuploidy. The word also appears as a noun for a cell or organism with such an abnormal count. Its antonym is euploid, meaning a genetically normal chromosome complement. Precise, clinical, and increasingly familiar through genetic screening discourse, aneuploid is essential vocabulary for anyone reading about genomics, reproduction, or cancer research.
Having a chromosome number that is not an exact multiple of the haploid number characteristic of the species.
"Karyotyping showed that the patient's leukaemic cells were highly aneuploid."
The dominant usage; almost always applied to cells, tissues, embryos, or organisms rather than people directly.
A cell, individual, or strain having an abnormally non-integral-multiple chromosome number.
"The culture became contaminated with aneuploids after several passages."
Used only when 'aneuploid' functions as a noun referring to cells or organisms with an abnormal chromosome count; the adjective form does not pluralize.
"The researchers sorted the euploids from the aneuploids under the microscope."
Most human embryos conceived naturally are thought to be aneuploid at some stage — one reason so many pregnancies end before anyone knows they began.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of aneuploid
Aneuploid was coined in early twentieth-century cytogenetics from Greek roots: the prefix 'an-' (not), 'eu-' (well or true), and '-ploid', derived from Greek 'ploion' or related forms meaning 'fold', as in 'many-fold'. The '-ploid' suffix was deliberately patterned on earlier terms like haploid, diploid, and polyploid when geneticists needed vocabulary for abnormal chromosome counts. Cognates within this family include euploid (a normal multiple of the haploid set) and aneuploidy (the state of being aneuploid).
Related word forms
How aneuploid is actually used
Strictly a technical term used in cytogenetics, genetics, oncology, and reproductive medicine; rarely encountered outside scientific writing. It functions chiefly as an adjective but is also attested as a noun naming an aneuploid cell or organism.
Easily confused with aneuploid
Haploid describes a normal single set of unpaired chromosomes (as in gametes), whereas aneuploid describes an abnormal total count that deviates from any whole multiple of the haploid set.
Polyploid cells carry extra complete sets of chromosomes (an exact multiple above diploid), while aneuploid cells have a partial gain or loss of individual chromosomes.
Euploid means having a normal, exact multiple of the basic chromosome set; aneuploid is its opposite.