Epigenetics

Epigenetics is the study of changes in the expression of genes in the deoxyribonucleic acid (DNA) of an organism that cannot be explained through common knowledge of DNA sequencing changes. Genes are the basic units within an organism's genetic code that transmit inherited characteristics from one generation to the next. Each gene is located on a fixed position on a chromosome. The primary understanding of epigenetics holds that changes on a chromosomal level can affect the way a gene activates or expresses itself. Some research has shown that the gene expression can then be inherited by the offspring of the individual in which the changes first occurred. The term epigenetics originally applied to the study of how fertilized zygotes mature into complex organisms. Over the years, epigenetics has come to recognize how genes can be altered by factors other than changes in gene sequence. By the twenty-first century, scientists had discovered epigenetic links to a variety of illnesses, behaviors, and other health statistics. As the study of epigenetics continued to develop, research began to indicate that multiple external influences were capable of affecting changes in genetic factors.

Background

The term epigenetics was originally used in scientific study of the unclear process by which a zygote, or a fertilized female reproductive cell, evolved into a mature organism. Eventually, epigenetics came to envelop developmental questions beyond the reproductive realm. The earliest inquiries into epigenetics drew from the nineteenth-century study of cell biology and embryology that would later lead to the modern awareness of the connection between genes and organism development. This early research and experimentation was focused on one central dilemma: how was it possible for one fertilized egg to turn into a developed organism with a variety of genetic characteristics?

The discovery of chromosomes in 1879 helped expand scientists' understanding of how organisms developed. Chromosomes are tiny, rod-shaped structures that carry the genes that determine the characteristics of an organism. Humans have forty-six chromosomes arranged in twenty-three pairs. Further research provided solid evidence that the mechanisms of development existed in the chromosomes. Scientists used fruit flies to create intricate chromosome maps that linked individual genes to specific chromosomes. Soon after came the discovery of the importance of DNA, the main component of all chromosomes and the carrier of genetic information. Scientists began to recognize that the way DNA was packaged within a chromosome influenced how genes would express themselves during development of an organism. As time went on, however, scientists also began noticing that changes to gene expression could be independent of DNA structure. At this point, it became necessary to distinguish between inheritable chromosomal changes erupting from changes in DNA and changes that were not a direct result of DNA sequencing changes. Those changes that did not occur due to sequence changes were labeled epigenetic.

The study of epigenetics further evolved in focus. The modern emphasis on nongenetic changes to chromosomal arrangement first took hold in the 1940s, when English embryologist Conrad Waddington proposed an answer to why cells take on different roles during the developmental stages of human life. Waddington believed that environmental factors led to changes in gene expression, and he was the first to use the term epigenetics to describe this process. As the decades passed, scientific experiments regularly observed strange patterns of chromosomal rearrangement that did not correspond to the DNA sequence of an organism. Many began to conclude that only outside influences could be responsible for these changes, and soon research was being geared toward understanding how external stimuli could influence gene function.

Overview

In the decades since epigenetics first came to the interest of the scientific community, experts have identified several epigenetic processes that have varying effects on an organism. These processes include methylation, acetylation, phosphorylation, ubiquitylation, and sumoylation. Each epigenetic process involves the addition of a chemical compound to an organism's genetic code that can alter a gene's function or activity. DNA methylation is the best known of these processes due to its relation to cancer development. Methylation involves the addition of a methyl group (a group of atoms derived from the natural gas methane) to a DNA molecule. The process was first linked to cancer in 1983 and has since been detected in many other diseases and health conditions.

Another process known as chromatin modification can also influence gene expression. Chromatin is the material that makes up a chromosome such as DNA, RNA (ribonucleic acid), and various proteins. When certain substances are introduced into chromatin, the structure can be modified to alter a gene's expression. In some cases, chromatin modification can shut down the expression of a gene entirely. This process can also have the opposite effect, however, and cause an otherwise dormant gene to express itself.

Such processes can lead to gene mutations. If these mutations damage a gene with a specific protective function, this can leave an organism susceptible to harmful microbes, toxic agents, and other dangerous substances. Although scientists had previously believed that epigenetic modification could be eliminated in later generations, contemporary research has shown that epigenetic changes could survive through at least four generations of an organism's lineage. This is known as transgenerational epigenetic inheritance. Several studies relating to this phenomenon have presented compelling results arguing that epigenetics plays an important role in which traits are passed down from generation to generation. Many of these studies trace epigenetic changes to environmental stressors such as food, air quality, and mental health. Research has proven that modified gene expression can be inherited in plants, but evidence showing the same inheritance in humans remained scarce. Research continued to extend the understanding of epigenetic processes within organisms. Many scientific disciplines have drawn from epigenetic literature to hypothesize its possible relation to an array of conditions, ranging from the medical to the psychological.

Bibliography

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