Olga Kovalchuk

Epigenetics has a lot to do with an organism’s interaction with the environment; therefore, it is important to review how our understanding of the interactions between the organism’s genome, surroundings, and phenotype has developed over time

There are multiple examples of the influence of environment on the genetic and epigenetic make-up of the organism. The phenomena of stress-induced transposon activation, non-targeted mutagenesis, stress-induced communication between cells and organisms, and evidences of transgenerational changes induced by stress are just some representations of epigenetic effects of the environment on the organism.

the most interesting examples of an epigenetically controlled process. It has already been known that a higher dose of mutagen does not necessarily result in a higher level of damage to DNA. In fact, low doses of ionizing radiation often lead to disproportionally high levels of DNA damage. Doses of ionizing radiation that are believed to have a negligible effect on a cell often exert dramatic influence on DNA damage and cell

Can organisms communicate memory of stress across generations? According to Darwin, organisms evolve from the pool of individuals with spontaneous changes/mutations through the process of natural selection. The process of mutagenesis is believed to be random, and the majority of mutations are deleterious. The rare mutations that become beneficial under certain environmental conditions have a chance to be fixed in a population. Because mutagenesis does not occur frequently, the fixation of desired traits would take place very rarely. In contrast, processes of acclimation and adaptation are rapid ones that allow organisms to acquire protection against stress in a single generation after stress exposure. These processes cannot be explained by the laws of Mendelian genetics. In this book, you find multiple examples demonstrating the inheritance of stress memory in various organisms across generations.

This chapter attempted to explain what epigenetics is, how it is involved in the regulation of growth and development of the organism, how it controls interactions of the organism with the environment, and what roles epigenetics plays in the mechanisms of inheritance and evolutionary processes.

There have been many more important discoveries in the field of epigenetics, and we apologize to all those authors whose work, though relevant, is not mentioned in this chapter because of limitations of spa

Methylation of DNA as an epigenetic modification is observed in organisms of all evolutionary levels—from prokaryotes to eukaryotes. However, there are differences in biochemistry, mediating enzymes and function. In bacteria and Archaea, the most abundant form is methylation of the N6 position of adenine, whereas in eukaryotes the prevalent modification is C5-cytosine methylation.

Histone proteins are the core of the chromatin organization. Although DNA methylation plays a significant role in regulating of chromatin structure and controlling gene expression, regulation via histone binding appears to provide a more drastic result and is by far more flexible. D

The question, “How do organisms pass on their acquired traits to the offspring?” has been around for perhaps 200 years. In 1866, the first substantial discovery was made by Gregor Johann Mendel who suggested that certain characteristics that determined the color of pea flowers, the shape of pea seeds, and other easily observable factors were passed from parental plants to their progeny. It took nearly 80 years until a factor responsible for a certain trait/phenotype was identified. In 1944, Avery, Macleod, and McCarty showed that transformation of the avirulent strain of Pneumococcus with DNA from the virulent strain made the former strain virulent, thus suggesting that DNA was a “causative” hereditary factor ().

The first RNAs that are not translated, thereafter referred to as non-coding RNAs (ncRNAs), were discovered in 1956 by Hoagland et al. who described transfer RNA (tRNA) as a carrier of amino acids. Another group of ncRNAs, ribosomal RNAs (rRNAs), was described by Scherrer et al. in 1963. Since then, the field of ncRNAs has expanded dramatically, and the current notion is that essentially the whole human genome is transcribed into RNA, with the majority of this being ncRNAs ().

Evolutionarily, ncRNAs involved in basic cellular processes, such as translation (tRNA and rRNA) or splicing (snRNA), are highly conserved. However, when it comes to ncRNAs with regulatory roles, post-transcriptional regulators, such as miRNA, are abundant in animals and plants, but it is not completely clear yet whether they exist in bacteria and Archaea.

As it is put by John Mattick, “The emerging evidence suggests that, rather than oases of protein-coding sequences in a desert of junk, the genomes of humans and other complex organisms should be viewed as islands of protein-coding sequences in a sea of regulation, most of which is transacted by RNA.”