mitotic crossing over

A process that results in genetic recombination occurring in somatic cells. It was first discovered as a rare event in Drosophila (fruit flies) but has since been found to occur in other organisms, especially fungi. In the latter, it sometimes occurs at a frequency that suggests it is a major source of genetic variation. The mechanisms involved are uncertain, since chromosomal pairing (a supposed requirement of crossing over in meiosis) is normally believed not to occur during mitosis.