Crossing over occurs frequently during meiosis. Can crossing over occur during mitosis? Explain why ...

Mitotic crossover is a rare event. Mitotic crossing over occurs only in diploid (somatic) cells; thus, to study mitotic crossing over in a haploid organism, diploid cells have to be created artificially. Mitotic crossing over most likely occurs when homologous chromosomal segments are accidentally paired in somatic cells since it requires that after DNA replication, but before homologous chromosomes randomly align along the metaphase plate, the homologous chromosomes come together and interact like chromosomes during prophase I in meiosis. Opportunities for this unusual kind of mitotic interaction are rare but variable by species. Although rare, mitotic crossing over is important in some organisms. Some fungi that do not have a sexual cycle use mitotic crossing over to introduce genetic variation. In humans, mitotic crossing over is thought to be important in allowing recessive cancer-causing mutations such as RB.