Which term does not describe an individual with Down syndrome?

An individual with Down syndrome is typically characterized by the presence of an extra copy of chromosome 21, which leads to the condition also known as Trisomy 21. This condition highlights that individuals with Down syndrome have three copies of chromosome 21 instead of the usual two, classifying it as a case of aneuploidy.

Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell, which can either be an excess or a deficiency. Therefore, individuals with Down syndrome fit into this category. Trisomy is a specific type of aneuploidy where there is an extra chromosome.

Monosomy, on the other hand, refers to the presence of only one copy of a particular chromosome instead of the standard two, which would not apply to Down syndrome. An individual with Euploid has the exact multiple of the haploid number of chromosomes, which is not the case for those with Down syndrome who have an abnormal chromosome count.

Thus, the term that does not describe an individual with Down syndrome is Euploid, as individuals with this condition do not have the normal diploid number of chromosomes.