Some mutations occur randomly and spontaneously during the process of mitosis or meiosis. Other mutations are caused by mutagenic agents, which are environmental or man-made factors that can increase the frequency of mutation. Environmental factors such as ultraviolet rays of the sun can cause changes in DNA that can lead to skin cancer. Cosmic rays from space that penetrate the earth’s ozone layer are also a cause of mutation. Ionizing radiation such as X-rays, gamma rays, and nuclear radiation produce free radicals (atoms with unpaired electrons) in the cell that can cause breaks in the DNA molecule. Carcinogens are chemical mutagens that cause gene mutations, which can result in cancer. A few examples of carcinogens are asbestos, benzene, some food dyes, and PCBs.
