Varieties of animals, plants, and microbes that are used in agriculture, industry and medicine are being continually improved by through breeding and research. One of the important methods used to genetically modify cells is the use of highly reactive chemicals that induce mutations in the DNA. While most mutations are detrimental or useless, breeders are often able to find mutations that improve the properties of an animal, microbe or crop plant. Many mutations occur without the involvement of chemical mutagenesis. These could include mutations generated by exposure of organisms to natural sources of UV light such as sunlight.