What roles do epigenetics play in gene expression, in what ways can these be observed in animal populations, and how might this pertain to human development?
DNA and genetic sequences have long been the standard for defining the process of adaptation within species, however new evidence has revealed a new source of variance over the last decade. Epigenetics have played a key role in generational variation and expedited adaptation in all forms of life and yet scientists have only recently begun to unravel its complexity. Epigenetics span many different areas of biology, touching life and evolution is several different ways; whether exploring the ways in which genotypes give rise to phenotypes, or the heritability of gene expression and change throughout generations epigenetics are an important source of adaptation (Bird 2007). The key mechanism which epigeneticists have proposed is that environmental factors can have lasting effects which can span generations on the genome without actual mutation (Bird 2007). As described by Rosenfeld, epigenetics can be defined as “a mitotically or meiotically heritable change in gene expression that occurs independently of an alteration in DNA sequence” (Rosenfeld 2009). This accurately highlights the most fascinating and valuable aspect of this science, it addresses the knowledge that DNA coding is not the sole contributor to development and that mutation is not the sole source of adaptation and variance. This is not important only for understanding development but also because it indicates an ability to modify the genome within a lifetime, an idea of great medical and biological importance. Epigenetic tags are heritable from cell to cell throughout its development causing effects on adult phenotype by the tags shifted in early life (Frésard et al 2013), which may suggest that markers found at childhood that predict disease may be changed and thus reduce risk of illness – a stunning prospect for the medical community. The applications of this new theory are already being tested on animals and have been documented occurring naturally in human populations. The possible advancements in human understanding and ability to control or use genetics for medical purposes are seemingly limitless; already the scientific community is making impressive advancements in this field.
It is important, when considering epigenetics, to understand the predicted mechanism driving these seemingly abnormal variance patterns. Additionally, one must understand that there is no ‘epigene’ but rather a researcher must observe the phenotype to understand the effects the meticulous tagging of DNA may have (Bird 2007). The researcher cannot simply break down codons and compute proteins, as the effects are seen whether a gene present is expressed. The process which are thought to play key roles in this turning ‘off’ and ‘on’ of genes are the histones, proteins which may cause the DNA to coil tightly to prevent transcription, and methylation marks, which also prevent transcription (Bird 2007). These, as will be discussed later, have been tested and observed in humans and other animals. In birds, Frésard describes an interesting pattern in which daughters born to dams from larger broods were smaller compared to their brothers, whereas if the dam was raised in a small brood the opposite is true (Frésard et al 2013). This trend in development which crosses generations is a stepping stone to understanding the abilities and constraints of epigenetic control. Such seemingly mundane facts give rise to significant trends. Interestingly, a similar effect has been studied in humans; children conceived during famine, called the HongerWinter children- after the event, showed increased risk of obesity across the board (Ahmed 2010). The trans-generational effect on the epigenetics of an individual in this instance is astonishing, showing that the eating habits of a previous generation can correlate to obesity in an offspring