Aneuploidy is a chromosomal variation due to a loss or a gain of one or more chromosomes resulting in the deviation from the normal or the usual number of chromosomes. The different conditions of aneuploidy are nullisomy (2N-2), monosomy (2N-1), trisomy (2N+1), and tetrasomy (2N+2).
Monosomy is a type of aneuploidy where there is a loss of a single chromosome of the normal complement. The chromosomal composition is represented by 2N-1. A cell or an organism exhibiting monosomy is referred to as monosomic. Monosomy may be caused by a nondisjunction during cell division, particularly meiosis. A partial monosomy can occur when only a portion of the chromosome is lost and therefore there is only a single copy of the chromosome while the rest has two copies. Examples of monosomy in humans are Turner syndrome (usually with one X chromosome only and the other is missing), cri du chat syndrome (where the end of the short p arm of chromosome 5 is missing), and 1p36 deletion syndrome (where the end of the short p arm of chromosome 1 is missing).
- monosomic (adjective, of, relating to, or characterized by, monosomy; noun, a cell or an organism in monosomy and a chromosomal composition designated as 2N-1)