Final answer:
Aneuploidy refers to the gain or loss of individual chromosomes that is not an exact multiple of a set. Monosomy is the loss of one chromosome, while trisomy is the gain of an extraneous chromosome. Individuals with aneuploidy may fail to develop or survive depending on the specific chromosome involved.
Step-by-step explanation:
An individual with an error in chromosome number is described as aneuploid, a term that includes 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 smaller chromosomes (13, 15, 18, 21, or 22) can result in offspring that survive for several weeks to many years.