Turner Syndrome: Monosomics are missing one copy of the chromosome.

The situation results from the presence of a single X chromosome(XO). In this syndrome, the Monosomics are missing one copy of a chromosome. In many diploid organisms, one chromosome copy is absent from a pair is deleterious. In humans, monosomies for any of the autosomes die in utero. 

Many X chromosome monosomies also die utero but some are viable. A human chromosome complement of 44 autosomes single X produces known as Turner syndrome, one copy of  Monosomics are missing a chromosome. 

In humans, monosomies for any of the autosomes die in utero. Many X chromosome monosomies also die in utero, but some are viable. A human chromosome complement of 4 autosomes plus a single X produces a condition known as Turner Syndrome represented as XO.