# Chapter 5: Mutations - how they arise and what to do with them

The classical experiments of Johann Gregor Mendel demonstrate how hereditary traits are passed on from generation to generation. Such experiments dealt with the inheritance of genetic information and led to the emergence of a new scientific field - genetics. However, further research has shown that genetic information can change, and this observation has led geneticists to begin studying the variability of living things.

Variability can be divided into heritable or nonheritable types. In non-heritable variability, the differences between individuals are caused by the influence of external environmental conditions. This type of variability is usually not passed onto offspring because it does not change the genetic information itself. Here, the environmental factors affect the structure of the proteins that the DNA wraps around (histones) or change how molecules bind to DNA. These are called epigenetic changes and sometimes these can be passed on to the next generation. You can learn more about epigenetics in Chapter 6 - How the Environment Can Affect Our Genes. Heritable variability is about changes at the level of the organism's genetic information, i.e., changes in the nucleotide sequence of the DNA molecule, which we call mutations. The term mutation was introduced by one of the rediscoverers of Mendel's laws, Hugo de Vries, who observed the appearance of new phenotypes in evening primrose plants (Oenothera lamarckiana). Initially, as offspring were clearly different from their parents, de Vries assumed that they were new species which were a result of spontaneous changes in traits. To describe their origin, de Vries introduced the term mutation in 1901 and postulated the “theory of mutation”, which, however, turned out to be not entirely correct. He assumed that mutations occur in batches and discontinuously, in contrast to Darwin's idea of gradual accumulation of new deviations from which selection chooses the most reproductive variants (you can learn more about Darwin's work in Chapter 14 - The principle of evolution). Experiments conducted in the following years showed that the Oenothera species were not the origin of a new species, but that the changes resulted from major rearrangements of chromosomes leading to new phenotypes, and the formation of new species in this way is rare.