Genes are genetic recipes. Edits that alter the recipe are epigenetic.
The term epigenetics is a portmanteau of genetics and epigenesis; coined by English geneticist Conrad Waddington in 1942 before details of genetics were known. Waddington meant epigenetics as a notion of how genes might interact with their environment to alter a phenotype: the visible traits of a cell or organism. While Waddington’s gist was generally correct, the definition of epigenetics has become more gene specific.
That gene expression may be suppressed by DNA methylation was discovered in 1975. It was not until the 1990s that the term epigenetics became common in research circles.
◊ ◊ ◊
Epigenetic mechanisms provide the key to understanding the size and organization of eukaryotic genomes. ~ American biochemist Nina Fedoroff
Epigenetics involve factors outside DNA sequencing by which life experiences are encoded into cells, and which may be passed on to cell offspring when a cell divides. Epigenetics provides for cellular memory that lives on in descendant cells.
Single-celled paramecia have 2 distinct mating types, called even (E) and odd (O). Sex between E and O occurs by conjugation: reversible cell fusion, during which partners exchange genes before separating into progeny cells.
Although offspring all start with identical, mixed genomes, each cell retains the memory of the mating type of its parent. It does so via epigenetics. Small RNA molecules communicate mating type between parent and progeny cells.
Epigenetics refers to regulating, modifying, or suppressing gene expression without altering DNA sequence, which instead would be a genetic mutation. Epigenetic effects also include changes to the chromatin proteins associated with DNA, whereby expression may be silenced or engendered.
Chromatin marks are highly specific and localized. They are induced by the signals cells receive during embryological development or in response to changed environmental conditions. Once induced, the information about cellular activities that is carried in a chromatin mark can often he transmitted in the cell lineage long after the inducing stimulus has disappeared. The chromatin-marking systems are therefore part of a cell’s physiological response system, but they are also part of its heredity system. ~ Israeli geneticist Eva Jablonka & English evolutionary biologist Marion Lamb
Epigenetics also encompasses modulating epigenetic effects. As such, epigenetics involves an interleaved context-dependent network that tempers gene expression. All epigenetic mechanisms are interrelated.
Genetically identical cells living in the same environment can display markedly different traits. Both extracellular triggers and internal influences can drive a cell to change its lifestyle or fate.
Genes do not automatically stay “on” or “off” once activated or repressed. Rather, those states of gene expression require the continual activities of the specific regulators to maintain that state of expression. ~ American molecular biologist Mark Ptashne
Epigenetic marks are an ongoing dynamic. Lifestyle and mental well-being have an epigenetic effect which is inherited by offspring.
We inherit more than just genes from our parents. Acquired environmental adaptations are passed to our offspring. ~ Italian geneticist Nicola Iovino
Memories are mental products, but they have physical correlates. Memories are epigenetically encoded via de novo protein synthesis. This holds for all organisms. These gene expression programs – memories – are readily transmitted to offspring.
Epigenetic processes mediate long‐term memory formation. ~ German molecular biologist André Fischer
Stress of any sort makes a deleterious mark that long outlasts its source. Conversely, meditation and a calm mind promote healthier genetic expression and boost the immune system.
Biologically based survival lessons are inherited. For instance, smells that signal danger are epigenetically encoded and transmitted to future generations.
Epigenetic changes are crucial for the development and differentiation of the various cell types in an organism, as well as for normal cellular processes. ~ English cytologist Alex Eccleston et al
Epigenetic activity guides organism development. This provides adaptive flexibility. The onset of mammalian puberty is epigenetically triggered. Epigenetic changes continue throughout an individual’s life.
Families tend to have similar epigenetic patterns. Handedness and sexual orientation are both familial epigenetic phenomena. Homosexual men have a different epigenome than heterosexuals.
Sexual orientation is implanted via epigenetic changes related to testosterone exposure during fetal development. These epigenetic marks are passed from one generation to the next.
Epigenetics explores how genetically identical entities, whether cells or whole organisms, display different characteristics, and how these are inherited. ~ French geneticist Jonathan Weitzman
◊ ◊ ◊
The cells themselves must be influenced ultimately by that mysterious force which we call life. ~ American physician Duncan Bulkley
Epigenetics is an integral part of the cell life cycle. All somatic cells retain the full complement of DNA present in germline cells and stem cells.
A stem cell generates a different cell type by invoking epigenetic alterations. The specialized functions of somatic cells are programmed epigenetically. That a somatic cell may differentiate into a different cell type in exigent circumstance is an epigenetic exercise of intelligence.
Various cell types respond differently to the environment by using distinct circuits of genomic reprogramming. ~ Italian biochemist Paolo Sassone-Corsi
Cells regularly adapt to changes in their environment by regulating gene expression, thus modulating cellular behaviors. Cell memory and intelligence are expressed by epigenetic responses.
Organisms have an array of strategies to recognize and restrain invasive foreign DNA, such as those introduced by viruses. One way is by remembering previous gene expression and tracking expression changes. This epigenetic memory silences foreign genes from one generation to the next.
Novel protein-coding genes can arise either through re-organization of preexisting genes or de novo. ~ French geneticist Anne-Ruxandra Carvunis et al
Occasionally, new genes are expressed. This activation is passed on as an epigenetic memory. Hence, a eukaryote may adopt a foreign gene, by a decision process not yet understood.
Plants and animals both produce many thousands of RNA molecules that do not code for proteins. Instead, these molecules may communicate the present state, and memories, thereby selectively silencing or promoting gene expression.
These RNA epigenetic messengers may travel from cell to cell, stifling or activating genes as they go. Hence, an epigenetic response to a stimulus may be carried far and wide from its point of origin.
For good or ill, epigenetic effects store an organism’s life experiences in chromatin. Behavior patterns, depravations, addictions, and illnesses, both physical and mental, are encoded epigenetically. Autism stems from epigenetic inheritance.
An organism lives an integrated experience. Hence, epigenetic marks are not isolated occurrences. Epigenetic changes may be different for different cell types, even as they emanate from the same experience.
Brain and nerve cells are affected by epigenetics. But the brain is not the origin of many behaviors, including those commonly considered as conscious choices. Impulses of all sorts are epigenetically encoded cellular imperatives from regions distant from the brain.
For better or worse, epigenetics provides the mechanism for lessons learned, neglected, or ignored. Being a creature of habit is embedded in cells. (As the mind-body is an entangled energetic gyre, trying to suss cause-and-effect between mind and body is like trying to untangle a gnarled enigma with imaginary tweezers.)
The external world, inclusive of food, toxins, carcinogens, and many other day-to-day factors, has a significant impact on cellular regulation. ~ American geneticist and cytologist Amber Willbanks et al
◊ ◊ ◊
Genes influence the behaviors of a cell and traits of an organism through the proteins and other molecules constructed from them. Getting from nucleotide code to bioproduct is a convoluted process where much can come out differently than DNA dictates.
Transcription comes first: making an RNA copy from DNA. Most epigenetic regulation happens by inhibiting transcription in very specific ways.
During translation, the RNA template is used to create a polypeptide, which is then folded up into an active protein during post-translational processing. These processes can render a functional protein quite different than what would be expected from reading the DNA recipe.
Hence, the genetic code alone provides only a partial picture of inheritance. Due to epigenetic influences, actions during protein synthesis and genomic activity during cell differentiation are as much effect as cause.
Germline cells erase epigenetic memory at critical points during development, thereby resetting the epigenome. But the erasure is commonly incomplete. Certain epigenetic indications escape reprogramming and are transmitted to offspring. By this, parental life experiences are passed to progeny.
Genes have adapted to allow for the correct balance of memory versus flexibility. ~ Indian epigeneticist Sandip De & American epigeneticist Judith Kassis
◊ ◊ ◊
Epigenetics is the story of a cell’s life experiences, of markings that are passed from one generation of cell to the next. Epigenetically, the offspring of organisms are simply an extension of cellular memory.
Most traits are the product of multiple genes, or even epigenetic tweaks to gene complexes. Few traits are traceable to a single gene. Even then, epigenetics factors in.