Final answer:
Aneuploidy is the condition described, resulting from nondisjunction during meiosis, leading to abnormal chromosome numbers such as in trisomy 21 or Down syndrome.
Step-by-step explanation:
Changes in the number of individual chromosomes such that the total number of chromosomes is not an exact multiple of a set results in a condition called aneuploidy. This happens due to mistakes during meiosis called nondisjunction, where homologous chromosomes or sister chromatids fail to separate properly, leading to gametes with an abnormal number of chromosomes. A common example of aneuploidy is trisomy 21, which causes Down syndrome.Aneuploidy is the condition described, resulting from nondisjunction during meiosis, leading to abnormal chromosome numbers such as in trisomy 21 or Down syndrome.