Organism having one chromosome pair less to the normal somatic complement of the species is

An organism having one chromosome pair less than the normal somatic complement of the species is Nullisomic.
Nullisomic is a genetic condition involving the lack of both the normal chromosomal pairs for a species (2n-2). Humans with this condition will not survive.
Nullisomy is caused by non-disjunction, during meiosis that causes two of the gametes to have no chromosomal material, leaving the other two gametes to have double the amount of chromosomal material.