Monosomy: the condition of having a diploid chromosome complement in which one chromosome lacks its homologous partner.
A trisomy is a chromosomal disorder characterized by an additional chromosome, so the person has 47 instead of 46.
Nullisomic is a genetic condition involving the lack of both the normal chromosomal pairs for a species (2n-2).
So, the correct answer is 'Monosomy'.
