What is the process called when homologous chromosomes exchange portions of their chromatids during meiosis?

The process during meiosis where homologous chromosomes exchange portions of their chromatids is known as crossing over. This occurs during prophase I of meiosis when homologous chromosomes pair up and form structures called tetrads. It is during this pairing that segments of genetic material are exchanged between non-sister chromatids, leading to a recombination of genetic information. This genetic recombination is crucial for increasing genetic diversity in gametes, which ultimately contributes to variation in offspring.

Independent assortment refers to the random distribution of maternal and paternal chromosomes into gametes during meiosis, while gene modulation pertains to changes in gene expression rather than chromosomal structure. Segregation describes the separation of alleles during gamete formation, which is related but distinct from the actual exchange of genetic material that occurs through crossing over. Hence, crossing over is the precise term for the exchange of portions of chromatids, facilitating genetic diversity in sexually reproducing organisms.