Final answer:
Non-disjunction during meiosis can lead to an incorrect number of chromosomes, resulting in genetic disorders like Down syndrome. Down syndrome occurs when there are three copies of chromosome 21. Factors such as the age of the mother can increase the risk of nondisjunction.
Step-by-step explanation:
Non-disjunction is an error in cell division that results in an abnormal number of chromosomes. This condition can lead to various genetic disorders, including Down syndrome, which is characterized by having three copies of chromosome 21, also known as trisomy 21. During meiosis, which is the process of cell division that creates gametes, chromosomes are supposed to separate and be distributed equally into the resulting sex cells.
However, nondisjunction occurs when the chromosomes fail to separate properly, leading to gametes with an extra chromosome or a missing chromosome.
When a gamete with an abnormal number of chromosomes fertilizes a normal gamete, the resulting zygote can have aneuploidy, which is a condition of having an abnormal number of chromosomes. In the case of Down syndrome, the extra copy of chromosome 21 leads to developmental and physical challenges for the individual.
Factors such as the age of the mother can increase the risk of nondisjunction; the older the mother, the higher the chance that an egg will have an incorrect number of chromosomes.