Final answer:
Nondisjunction occurs when chromosomes do not separate properly during meiosis, potentially resulting in gametes with abnormal chromosome numbers. It can occur during meiosis I with homologous chromosomes or during meiosis II with sister chromatids, leading to genetic disorders in offspring.
Step-by-step explanation:
Nondisjunction occurs when chromosomes do not separate properly during meiosis. This process can lead to gametes with an abnormal number of chromosomes, specifically resulting in n+1 (one extra chromosome) or n-1 (one missing chromosome). There are two critical points during meiosis where nondisjunction can occur:
- If homologous chromosomes fail to separate during meiosis I, two gametes will lack that chromosome, whereas the other two will have two copies of it.
- If sister chromatids fail to separate during meiosis II, one gamete will lack that chromosome, two will have a typical single copy, and one will have two copies.
Both scenarios lead to the production of gametes with abnormal chromosome numbers, which can cause genetic disorders in offspring, such as Down syndrome, when these gametes fuse with a normal gamete during fertilization.