Final answer:
Nondisjunction can occur during both meiosis I and II, leading to gametes with an abnormal number of chromosomes. Homologous recombination, a different process, occurs to facilitate genetic diversity, and is also used for DNA repair.
Step-by-step explanation:
The correct statement about nondisjunction is that it can occur when homologous chromosomes do not separate during meiosis I, or when sister chromatids do not separate during meiosis II. This results in the formation of gametes with an abnormal number of chromosomes, specifically n+1 (one extra chromosome) or n-1 (one less chromosome). Homologous recombination, however, is a separate process that occurs during Meiosis I and is necessary for generating genetic diversity through the exchange of alleles between paired homologous chromosomes. DNA breakage and the subsequent exchange of alleles are vital steps in this process. Additionally, recombination machinery is used both for this process during meiosis and for DNA repair during the cell cycle.