Epigenetics refers to the process of regulating gene expression by altering chemical modifications on the histone proteins or DNA itself to control the compaction of the chromatin. In general, genes located in tightly compact heterochromatin are not expressed and genes in more loosely arranged euchromatin are readily expressed. Epigenetic modifications can control gene expression, allowing genes to be switched ‘on’ or ‘off’ in response to different environmental stimuli. These changes to chromatin include a wide range of DNA and histone modifications including: nucleotide or histone methylation and histone acetylation, ubiquitination and citrullination. Many modifications to different histone proteins have been identified and the interaction between these modifications are often complex and are referred to as the “histone code”.
Environmental influences can cause epigenetic changes; diet, lifestyle and exposure to chemicals and pollutants can all cause changes the epitome of an individual. Epigenetic studies are important in the ‘nature vs nurture’ debate, with results showing that environmental factors can have a direct impact on expressed phenotype without altering the DNA sequence.