Final answer:
Meiosis I involves crossover and the separation of homologous chromosomes, while these processes do not occur in meiosis II.
Step-by-step explanation:
In meiosis I, several events occur that do not happen in meiosis II. One of the main differences is the pairing and exchange of genetic material between homologous chromosomes, which is known as crossover. This process generates new combinations of genes on the chromatids. Additionally, meiosis I involves the separation of homologous chromosomes into different nuclei, resulting in a reduction in ploidy level. Meiosis II, on the other hand, is more similar to mitosis and involves the separation of sister chromatids into four haploid sex cells.