The condition of having a diploid chromosome complement in which one chromosome lacks its homologous partner is called

Monosomy

Explanation:

Monosomy is a condition in which there is an absence of one chromosome from the pair of chromosome in an individual's karyotype. The human karyotype consists of 46 chromosome, but in the case of monosomy, which is the absence a chromosome, such individual will possess 45 chromosomes.

Females possess two XX chromosomes, but in the case of monosomy, the female has just one X chromosome instead of two.

Monosomy results to certain human genetic conditions like Turner syndrome.