Mutant Isolation

Go to: Laboratory Project Overview -- General Methods -- Mutant Isolation -- Screening Procedures -- Access to Databases -- Writing a Research Proposal -- Making Posters

You will be provided with a supply of Arabidopsis seedlings from which to isolate mutants. The seeds, purchased from Lehle Seeds (Tucson, AZ) were produced by plants which had been treated as seeds with the chemical mutagen ethyl methane sulfonate (EMS). They are thus designated M2 seeds (mutagenized F2). EMS introduces point mutations randomly in the genome. If a point mutation occurs in a critical portion of a functional gene, a mutant phenotype may result. Because physiological processes are usually governed by the products of numerous genes, the same mutant phenotype may result from independent mutations at different locations in the genome. Conversely, some proteins are so important to the plant that multiple copies of the gene may exist. A mutation in any one copy would probably have no effect on the plant and therefore you will never isolate such a mutant. Some mutants may be lethal and will never be isolated. Others will cause only slight changes in phenotype and may not be detected. Mutations in "unused" or non-critical DNA will probably have no effect on the plant's phenotype.

Since plants are diploid, mutant phenotypes are rarely expressed in the M1 generation. Because Arabidopsis is self fertile, allowing the M1 plants to flower and set seed results in an M2 generation in which 25% of the seeds from a given plant are homozygous for a mutant allele and would thus express the mutant phenotype. These mutants can then be isolated using various screening procedures. The screen you use must be carefully designed so as to isolate only the type of mutant you are looking for. For example, a small phenotype could be produced by hundreds of different mutations. Screens generally involve either looking for abnormal plants when seedlings are grown under normal conditions, or conversely, looking for normal plants when seedlings are grown under abnormal conditions.

Go to: Laboratory Project Overview -- General Methods -- Mutant Isolation -- Screening Procedures -- Access to Databases -- Writing a Research Proposal -- Making Posters

James Madison University, Department of Biology
Jonathan D. Monroe, PhD
Comments to author: monroejd@jmu.edu