Overview

Mutations are essential tools for the science of genetics. Mutations are required to discover a gene and establish its identity, to learn what genes affect a particular phenotype, and to determine the relationship between a gene's structure and its function. Mutations have practical applications in studying genetic disease and in improving organisms used for food, fiber, or valuable molecules.

A mutation is not usable until a strain of organisms carrying that mutation is established. The selection and isolation of mutant strains of any organism require special procedures; examples are described in this chapter.

Because mutation is a fundamental genetic process, geneticists need sensitive, reliable, efficient methods of measuring mutation rates. One such method, devised to screen chemicals for mutagenicity, is the Ames test.

Sources of New Mutations

Natural populations are treasure troves of mutations. Most natural mutations are rare but can be recovered by selection screens, experiments designed to separate organisms that carry mutations in a specific gene or locus.

A second way to get novel mutations is to induce them in organisms, using chemical mutagens, radiation, or genetically engineered transposons. Mutagens increase the rates of random mutation, often by 1000-fold or more. As with natural mutations, a selection screen must be used.

When a gene has been cloned, new mutations can be induced in a controlled way by in vitro mutagenesis. The idea here is to target specific DNA sequences within the gene for change, rather than to make random changes.