Final answer:
The most common aneuploidy seen in living humans is Down Syndrome, which is caused by an extra copy of chromosome 21.
Step-by-step explanation:
An individual with an error in chromosome number is described as aneuploid. The most common trisomy among viable births is that of chromosome 21, which corresponds to Down Syndrome. Individuals with this inherited disorder are characterized by short stature and stunted digits, facial distinctions that include a broad skull and large tongue, and significant developmental delays.