What term describes the absence of one chromosome from a pair?

The term that describes the absence of one chromosome from a pair is monosomy. In humans, this condition results in only one chromosome present instead of the typical two in a pair. Monosomy is often associated with various genetic disorders and can have significant phenotypic consequences.

In contrast, trisomy, which is another option, refers to the presence of an extra chromosome, leading to three copies instead of two. Euploidy refers to a complete set of chromosomes being present, while polyploidy denotes a condition where there are more than two complete sets of chromosomes. Both euploidy and polyploidy do not reflect the absence of any chromosome but rather imply an increase in the number of chromosome sets.