Much has been learned in the life sciences in the last several decades about how an organism can alter its genome to enable it to adapt to new environmental conditions. Transposable genetic elements were discovered some seventy years ago by Barbara McClintock (McClintock 1941, 1950, 1955, 1956, 1983), but they were initially dismissed by mainstream geneticists as spurious phenomena. McClintock pursued her research despite it being considered a backwater area, and eventually the importance of her work was recognized by the Nobel Prize committee in awarding her the Prize in Medicine in 1983.
The transposable genetic elements she discovered have been subsequently revealed to be members of a class of genetic rearrangements that do not occur spontaneously by chance but are under strict cellular control. In these rearrangements, sections of DNA can move from one place to another in the genome, or can be removed entirely. These controlled genetic changes can reveal latent genes that were in the genome but were previously unavailable to the organism. Hall (1999) has called them cryptic genes, but more about these genes later.
Environmental changes are known to elicit various kinds of stress in an organism. Furthermore, McClintock noticed in her early work in plants that some types of stress can trigger genetic rearrangements (McClintock 1984). Organisms seem to have the ability to relieve the stress by altering both their phenotype and genotype. Stress has been defined generally as an environmental condition threatening to upset the balance and stability of the organism. Stress in an organism includes many kinds of stimuli. In microorganisms, stress can be an excess or deprivation of necessary molecules, such as sugars or salts. It could also be excessively high or low temperature.
In plants and animals, stress is usually a more complex form of environmental insult. Stress can elicitgenetic rearrangements, which can in turn activate latent (or cryptic) genes. Many examples are known of genetic rearrangements activating latent genes (e.g., Shapiro 1992 & 2009, Hall 1999). Slack et al. (2006) have reported that stress can elicit an adaptive response in E. coli by selectively amplifying genes. Hersh et al. (2004) have reported that stress can induce adaptive genetic changes in E. coli. In subsequent sections I will discuss stress in both single-celled and higher organisms, and its heritable effects. (P. 47)
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