Monosomy is the state of having a single copy of a chromosome pair instead of the usual two copies found in diploid cells. Monosomy can be partial if a portion of the second chromosome copy is present. Monosomy, or partial monosomy, is the cause of some human diseases such as Turner syndrome and Cri du Chat syndrome.


Monosomy is used to refer to a status of an autosomal gene, when normally two copies are supposed to be present and instead only a single copy of a gene is present. This word can also refer to multiple genes or segments, or even an entire chromosome, where an individual is supposed to have two copies of this gene or chromosome, and they only have a single copy. The loss of one of two copies of an autosomal gene or segment of genes, or an entire chromosome, is a cause of human genetic disease.

- Leslie G. Biesecker, M.D.