Final answer:
Nondisjunction during meiosis can result in gametes with an abnormal number of chromosomes, leading to chromosomal disorders such as trisomy 21, commonly known as Down syndrome.
Step-by-step explanation:
During meiosis, if two chromosomes do not separate correctly, a phenomenon known as nondisjunction occurs. This can happen in either the first or second division of meiosis. When nondisjunction occurs during meiosis I, homologous chromosomes fail to separate, which results in two gametes that lack a chromosome and two gametes with an extra chromosome.
Conversely, if nondisjunction occurs during meiosis II, it's the sister chromatids that fail to separate. This leads to one gamete without the chromosome, two gametes with the correct number, and one gamete with an extra chromosome. Such errors can lead to chromosomal disorders, as seen in conditions like Down syndrome, also known as trisomy 21, where an individual has an extra chromosome 21.
Most of the time, a zygote with an abnormal chromosome number will not survive. On the occasions they do, the individual will likely present with serious genetic disorders.