1. High temperature: High temperature and radiation increase the tendency of crossover occurrence. Siddique Publications
2. Aging: As the organism ages, the incidence of crossing over decreases.
3. Mutation: The level of crossing over is reduced due to mutation.
4. Inversion: Inversion stops the crossing over process.
5. Interference: Interference with the formation of another chiasm near the site of chromosomal formation. This phenomenon is called interference.
6. Radiomimetic substances: Chemical substances that increase the rate of somatic crossing over are called radiomimetic substances. Eg- ethylmethane sulphonate. Dr. Siddiq Publications
7. Chemicals: Various chemicals reduce crossover. For example, colchicine, selenium, etc. Dr. Siddiq Publications