Alteration in the genetic material of a cell that is transmitted to the cell's offspring. Mutations may be spontaneous or induced by outside factors (mutagens). They take place in the genes, occurring when one base is substituted for another in the sequence of bases that determines the genetic code, or when one or more bases are inserted or deleted from a gene. Many mutations are harmless, often masked by the presence of a dominant normal gene (see dominance). Some have serious consequences; for example, a particular mutation inherited from both parents results in sickle-cell anemia. Only mutations that occur in the sex cells (eggs or sperm) can be transmitted to the individual's offspring. Alterations caused by these mutations are usually harmful. In the rare instances in which a mutation produces a beneficial change, the percentage of organisms with this gene will tend to increase until the mutated gene becomes the norm in the population. In this way, beneficial mutations serve as the raw material of evolution.
Learn more about mutation with a free trial on Britannica.com.
PCR mutagenesis is simple method for generating Site-directed mutagenesis. This method can generate mutations (base substitutions, insertions, and deletions) from double-stranded plasmid without the need for subcloning into M13-based bacteriophage vectors and for ssDNA rescue. The procedure involves a PCR reaction using a supercoiled plasmid vector as the template and two synthetic oligonucleotide primers containing the desired mutation with each complementary to the opposite strands of the vector. After PCR, the template (wild type) plasmid which is dam methylated in almost all E. coli is removed by digestion with Dpn I which is specific for methylated DNA. The mutated plasmid remains intact in the reaction.