What is "aneuploidy"

abnormal number of chromosomes, 1934, from aneuploid (1931), Modern Latin, coined 1922 by G. Täckholm from an- (1) "not" + euploid, from Greek eu- "well, good" (see eu-) + -ploid, from ploos "fold" (see -plus) + -oid.

n. (context genetics English) The condition of being aneuploid; the state of possessing a chromosome number that is not an exact multiple of the haploid number of the organism in question.

n. an abnormality involving a chromosome number that is not an exact multiple of the haploid number (one chromosome set is incomplete)

Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example when having 45 or 47 chromosomes when 46 is expected in a human cell. It does not include a difference of one or more complete sets of chromosomes, which is called euploidy. An extra or missing chromosome is a common cause of genetic disorders, including some human birth defects. Some cancer cells also have abnormal numbers of chromosomes. Aneuploidy originates during cell division when the chromosomes do not separate properly between the two cells.

Different species normally have different numbers of chromosomes from one another, and the terms "aneuploid" and " polyploid" refer to the chromosome number being different from the usual number for that species.

Chromosome abnormalities are detected in 1 of 160 live human births. Apart from sex chromosome disorders, most cases of aneuploidy result in death of the developing fetus ( miscarriage); the most common extra autosomal chromosomes among live births are 21, 18 and 13.