Final answer:
The most common aneuploids in humans are trisomies, with the most notable example being Down Syndrome on chromosome 21.
Step-by-step explanation:
In humans, an individual with an error in chromosome number is called aneuploid. Aneuploidy can include monosomy (loss of one chromosome) or trisomy (gain of an extraneous chromosome). Monosomic human zygotes missing any one copy of an autosome invariably fail to develop to birth because they lack essential genes. Most autosomal trisomies also fail to develop to birth; however, duplications of some of the smaller chromosomes (13, 15, 18, 21, or 22) can result in offspring that survive for several weeks to many years. The most common trisomy among viable births is that of chromosome 21, which corresponds to Down Syndrome.