Final answer:
During meiosis, crossing over occurs when homologous chromosomes exchange segments of genetic material, increasing genetic diversity among gametes.
Step-by-step explanation:
During meiosis, crossing over occurs during prophase I when homologous chromosomes pair up and exchange segments of genetic material. This process, also known as genetic recombination, increases genetic diversity among the resulting gametes. Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes, resulting in new combinations of genes on each chromosome.