1) The presence of only one chromosome from a pair; partial monosomy refers to the presence of only one copy of a segment of a chromosome.

2) 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.