Final answer:
Crossing over, also known as recombination, is the process during prophase I of meiosis where homologous chromosomes exchange segments, resulting in genetic diversity.
Step-by-step explanation:
The process where portions of homologous chromosomes exchange segments with one another is known as crossing over or recombination. This event occurs during prophase I of meiosis when homologous chromosomes synapse and form a configuration known as a tetrad. During this stage, non-sister chromatids come into close contact and exchange genetic material. This exchange can occur multiple times, leading to a unique combination of genes. These points of contact and exchange are visible under a microscope as chiasmata. The genetic reshuffling that occurs due to crossing over is crucial for genetic diversity as it combines maternal and paternal alleles onto the same chromosome.