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Noninduced Mutagenic Agents, Creating Mutations, The First Mutagenesis Assay, Detecting Mutations

Mutagenesis is the process of inducing mutations. Mutations may occur due to exposure to natural mutagens such as ultraviolet (UV) light, to industrial or environmental mutagens such as benzene or asbestos, or by deliberate mutagenesis for purposes of genetic research. For geneticists, the study of mutagenesis is important because mutants reveal the genetic mechanisms underlying heredity and gene expression. Mutations are also important for studying protein function: Often the importance of a protein cannot be characterized unless a mutant can be made in which that protein is absent.

Assays for Chromosome Aberrations.

Chromosomal aberrations can be detected by examining cells in mitosis or meiosis for changes (see Figure 2). Typically, bone marrow cells of mice or rats are examined for in vivo tests. Any cells can be used for tests of cells in culture, but Chinese hamster cells or human fibroblasts are most commonly used. Another test, called the micronucleus test, is also commonly used. Micronuclei are small nuclei that arise from pieces of chromosomes or whole chromosomes that have been lost during cell division. They are conveniently detected in mouse red blood cells, which have no normal nucleus but which often retain micronuclei. The micronucleus assay is also widely used in cultured cells.

Assays for Somatic Mutations.

Recessive mutations can be detected more readily on a mammalian X chromosome than on the other chromosomes, because only one X chromosome is active. Therefore, detection of the mutagenic potential of a substance in mammals can be most efficiently performed by analyzing the X-linked mutations. A system using the X-linked gene hprt has been widely used because the enzyme is not essential and because the addition of the drug thioguanine kills all cells except mutants. A count of the cells that can be cultured in the presence of thioguanine is a count of hprt mutants.

John Heddle


Griffiths, Anthony J. F., et al. An Introduction to Genetic Analysis. New York: W. H.Freeman, 2000.

Muller, Hermann J. "Artificial Transmutation of the Gene." Science 66 (1927): 84-87.

Rubin, G. M., and A. C. Spradling. "Genetic Transformation of Drosophila withTransposable Element Vectors." Science 218 (1982): 348-353.

Internet Resource

United Nations Scientific Committee on the Effects of Atomic Radiation. <http://www.unscear.org/>.

Michael Smith of Canada received the 1993 Nobel Prize in physiology or medicine for invention of site-directed mutagenesis. He shared the prize with Kary Mullis, who invented the polymerase chain reaction.

Additional topics

Medicine EncyclopediaGenetics in Medicine - Part 3