Final answer:
Nondisjunction is the failure of chromosomes to separate during meiosis and leads to aneuploidy, which is an abnormal chromosome number. This can result in gametes having too many or too few chromosomes.
Step-by-step explanation:
Nondisjunction is the failure of homologous chromosomes to separate during meiosis I or the failure of sister chromatids to separate during meiosis II. This results in an abnormal chromosome number, a condition known as aneuploidy. Aneuploidy occurs when gametes have too many or too few chromosomes due to nondisjunction. For example, if a homologous pair fails to separate during meiosis I, the resulting gametes can have n+1 or n-1 chromosomes instead of the normal n number of chromosomes.