Directed mutagenesis, also known as directed mutation, is a largely discredited hypothesis proposing that organisms can respond to environmental stresses through directing mutations to certain genes or areas of the genome.
The hypothesis was first proposed in 1988 by John Cairns, of Harvard University, who was studying Escherichia coli that lacked the ability to metabolize lactose. He grew these bacteria in media in which lactose was the only source of energy. In doing so, he found that the rate at which the bacteria evolved the ability to metabolize lactose was many orders of magnitude higher than would be expected if the mutations were truly random. This inspired him to propose that the mutations that had occurred had been directed at those genes involved in lactose utilization.
Later support for this hypothesis came from Susan Rosenberg, then at the University of Alberta, who found that an enzyme involved in DNA recombinational repair, recBCD, was necessary for the directed mutagenesis observed by Cairns and colleagues in 1989.
However, the directed mutagenesis hypothesis was essentially disproved in 2002, when John Roth and colleagues showed that the phenomenon was due to general hypermutability due to selected gene amplification, and was thus a "standard Darwinian process."
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