Crossing over is a process that occurs during meiosis, not mitosis. The primary reason for this lies in the different purposes and outcomes of these two types of cell division.
Mitosis is responsible for producing two genetically identical daughter cells from a single parent cell, primarily for growth, repair, and asexual reproduction. Since the goal of mitosis is to maintain the same genetic material, there’s no need for the exchange of genetic material between homologous chromosomes.
In contrast, meiosis is the process that leads to the formation of gametes—sperm and eggs—in sexually reproducing organisms. One of the key features of meiosis is the exchange of genetic material between homologous chromosomes during prophase I, known as crossing over. This process increases genetic diversity in the offspring by reshuffling parental genes.
To summarize, crossing over is specifically aligned with gamete production and genetic diversity, which is not a requirement in the straightforward cellular replication that occurs in mitosis.