Our genome is established when fertilization takes place, and the code remains unchanged throughout our life, except for mutations that may occur in individual cells. Nevertheless, the previous page outlined many internal mechanisms that operate to control the expression of specific genes. In addition, we now know that many external factors (epigenetics) can affect the timing of the gene expression, the degree of expression, and the eventual phenotype that is expressed. These external factors can produce small modifications to DNA, such as addition of metal ions, addition or removal of acetyl groups or methyl groups to DNA or to the histones that control the wrapping and packing of DNA. Attachment of methyl groups appears to reduce transcription or even shut it off; attachment of acetyl groups to histones turns genes on. These biological changes to the genome is known as 'epigenetic factors', i.e., changes occurring above the level of the genome.

The methyl group

The methyl group -CH3

The acetyl group

Modification of DNA by the methyl group:

In essence, the DNA in our cells provide the code for making functional proteins, and the epigenetic factors act as switches which turn genes off and on. Epigenetic factors are likely to play many important roles, such as:


Epigenetics and the Influence of Our Genes

This is an 18:40 min video from TEDxOU by Courtney Griffin that provides an excellent explanation of the interaction among:

 In summary, all of our traits and characteristics (our phenotype) are the result of an interaction between our genome (all of the genes we inherit) and environmental factors. Some environmental factors (including our diet, our behaviors, and a myriad of environmental exposures) influence our phenotype through non-genetic mechanisms. For example, one might have a number of genes that predispose an individual to being lean; however, such an individual might still become overweight or obese despite their "lean genes" as a result of chronically overeating. Yet other epigenetic factors from the environment can modify the genome in subtle ways without actually changing the code.

For more information on epigenetics explore the following web site: http://learn.genetics.utah.edu/content/epigenetics/

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