Inspecting the history of organismal lineages as depicted by The Tree of Life can lead to the popular belief that the human species is the most complex out of the 5 to 100 million species inhabiting Earth. Yet, how accurate is this statement? Does it seem unorthodox that a microscopic water flea is fundamentally more complex than a human being? The human species is made up of an estimated 25,000 to 30,000 genes, a number that, although modest, falls significantly short from the original predictions. If the number of genes is not an indicative of an organism's overall complexity, to what biological system does the human species owe its widespread phenotypic diversification? Welcome to the fascinating world of epigenetics!
The Human Genome Project is an undeniable advancement in the history of biological sciences. Scientists from all over the world compiled a vast number of research projects with the cumulative purpose of offering a complete map of the genes composing the human genome, one that would facilitate further understanding of how genes behave within the human species. Despite its significance, recent studies have put into question whether this map is able to explain the complexity of the genome on its own, and whether biological factors other than DNA sequence serve as prime regulators of genetic expression. These biological factors compose what can be categorized as a second layer of biological activity known as the epigenome, which works hand in hand with the DNA sequence to regulate the overall expression of genes and also protect genome's integrity.
Epigenetic markers include many modifications, ranging from DNA methylation to the deposition of histone variants in chromatin, ultimately defining chromatin state in a reversible and potentially heritable matter. Furthermore, epigenetic modifications respond to environmental factors, thus establishing a bridge between the outside world and the genome. The possibility of a genome actively corresponding to its surroundings via epigenetic mechanisms has led to a heightened interest in learning how environmental factors could “imprint” DNA. This means that an ancestor’s past exposure to certain environmental conditions such as substance abuse can trigger an avalanche of epigenetic mechanisms that engrave an environment-determined genetic state on the genome, thus imprinting the condition even in future generations. The developmental stage at which these imprinted modifications are activated in future generations and the magnitude of the genetic effect varies greatly; nevertheless, studies are providing evidence on how these effects account for genetic expression abnormalities early in fetal development. These findings concerning the existence of an epigenome are, consequently, of esteemed importance because they bestow a responsibility for the protection of genomes and well-being of future generations.
Epigenetic markers include many modifications, ranging from DNA methylation to the deposition of histone variants in chromatin, ultimately defining chromatin state in a reversible and potentially heritable matter. Furthermore, epigenetic modifications respond to environmental factors, thus establishing a bridge between the outside world and the genome. The possibility of a genome actively corresponding to its surroundings via epigenetic mechanisms has led to a heightened interest in learning how environmental factors could “imprint” DNA. This means that an ancestor’s past exposure to certain environmental conditions such as substance abuse can trigger an avalanche of epigenetic mechanisms that engrave an environment-determined genetic state on the genome, thus imprinting the condition even in future generations. The developmental stage at which these imprinted modifications are activated in future generations and the magnitude of the genetic effect varies greatly; nevertheless, studies are providing evidence on how these effects account for genetic expression abnormalities early in fetal development. These findings concerning the existence of an epigenome are, consequently, of esteemed importance because they bestow a responsibility for the protection of genomes and well-being of future generations.
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