monosomic

An organism deficient in one chromosome from an otherwise diploid set, i.e. 2n-1. Monosomy typically arises by fertilization occurring between a normal gamete (n), and one deficient in the said chromosome (n-1). Monosomics are more common in polyploids where the deleterious consequences of missing a chromosome can be masked by chromosomes in other genomes. See aneuploidy.